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STATE OF CALIFORNIA DEPARTMENT OF WATER RESOURCES DIVISION OF RESOURCES PLANNING
STATE WATER RESOURCES BOARD BULLETIN NO. 18
Volume I TEXT AND PLATES
SAN LUIS OBISPO COUNTY INVESTIGATION
GOODWIN J. KNIGHT HARVEY O. BANKS Governor Director of Water Resources
UNlVhKSITY OF CAU DAVIS May, 1958 L
STATE OF CALIFORNIA DEPARTMENT OF WATER RESOURCES DIVISION OF RESOURCES PLANNING
STATE WATER RESOURCES BOARD BULLETIN NO. 18
SAN LUIS OBISPO COUNTY INVESTIGATION
Volume I TEXT AND PLATES
GOODWIN J. KNIGHT |%^fS^5Bl HARVEY O. BANKS '':-. > Governor \ \ i ':^kM$
May, 1958
-P \7?V
^ RNiX
.
TABLE OF CONTENTS
Page
LETTER OF TRANSMITTAL, STATE DEPARTMENT OF WATER RESOURCES . . . xiii
ACKNOWLEDGMENT . .. • xiv
ORGANIZATION, CALIFORNIA WATER COMMISSION . * * ...... xv
ORGANIZATION, STATE DEPARTMENT OF WATER RESOURCES ...... xvi
OBGANIZATION, COUNTY OF SAN LUIS OBISPO,
BOARD OF SUPERVISORS • e c & o # * • e • o * • •999 xviii
CHAPTER I INTRODUCTION
Authorization for Investigation *•«»£> 909OO 2
Related Investigations and Reports « o • • • o
Scope of Investigation and Report • 8
Area Under Investigation »»• *•«*•*«« *•••#••«* » 1U
Drainage Basins • «« <>•«•••<>« O0««0*»*0 « • C Ik
U-Lirna i»e oo • oo»*o«*ooo6o 17
Geology ••••••«•«•••• . 18
OOXJ.S *co.*ooo »•«». o»» 19
Present Development •••••*«•• 21
Hydrologic Units • ••«••*•»•••• »•»»•» 26
CHAPTER II WATER SUPPLY 28
Precipitation cooft*««o»o«oo9* • •oo«e»*9«t< 30
Precipitation Stations and Records • <, « • • • O O 30
Precipitation Characteristics O o « n o • • • ••0 9
Runoff o . . OOO'.*»Ofcc09O«OO««»»OC»Or>»9 • iiO
Stream Gaging Stations and Records la
Runoff Characteristics •••••. k$ has. III! V
Quantity of fas&bSt • ««••«• .»....©*.><..*«, U8
Major Exchanges «t Ifeter o o » © « ..- a * »• » „„.<*<».*.. . 5^
Underground Hydrology * -© c © * « » © * t 4 i ...... „ 53
»'•• Upper Salinas Unit «'*«- «"t » .<* * f.-.^ ,* * '*'•*.•»»,** * 62
Pa&o Robl«B Basin * » *©«.»«• « * © « « ,. e » « < . , . «
Peso Basin and . Miscellaneous Ground
o (C- to '. - a- o I^OU-TC^H* O O « a * O c- [ • * . . . .
Coast ai a © » » * a «. , . » .. - - - ,...... 67
Cambria Subviiri t o*.©*©. *..»•***»•«*..„ 6t'
San Luis Obispo £ubuniv, «<-« • a * © » •;».'.% © * * * „ * . . * 70
*''.*-„» Arroyo Grande Subunit » * ;• * « 4 «• * * * * * * . » 4 73
Santa Maria Unit © © © , < »»..<-, „ »©•*««« . . s „ . „ 77
Guyana Unit » o • © e * e . © < ...»,.... © • • * . • . 78
Carilzo Plain Unit * © . © » * * * » .. . . t. . » . c « „, , . „ . 79
San Joaquin Unit ©••>;. * •> © c * * o ..<*„.,..« e „<,„. „ 3<-?
- '» Quality of Mater 9 > «* 9 # s » >* * » o <» » * * • %. 4 * # » .* ,* 03 (
Standards of Vteter Quality » © © © » * » * * . s . s , , .. . „ 81*
Irrigation Use » © * © * © o » * « -.. «.*.».«„<.(. <* CI4
Domestic and Municipal Tme „ , * * . » , , i . . . , „ 87
,&-*.-•»• '*>•>' '#••* Industrial ties * * » * - * * v - »- « « » * 89
Quality of Surmise Mater © © * o © © . * * . . . ,.,..«, 90
Quality of Groutid. Jator © © © <, ©©.»..«.-,..,. o . <> 9h
Sources of Impairment of Hates' Quality *. • « * .« « : .> **«#,» 97
Natural Souroee it t • .> > ,a .* «.* ......
Domestic Sei«ege . © * * » * » • ».,.,...> « 1 # ».,* • ?9
Irrigation Return ©.©.,,.,.... 90 Industrial Wastes ...... 100
Sea-Water Intrusion . . . o <> . . . . o . . o ...... 100
CHAPTER III. WATER UTILIZATION AND REQUIREMENTS 102
Present Water Supply Development . . o . . . • ...... 105
Major Water Supply Developments . . . . , ...... 105
Water Service Agencies ...... <> . . > . . 110
Appropriation of Water ...... 11^
Dams Under State Supervision o = ...... 115
JjCLDCL U S6 oooooooooooooooooooooooooooo© X J.O
XTrcSGIlTi jjfiUP U Sc 0OO»0OO000O«OO 00000*000 XXO
X Probable Ultimate Pattern of Land Use ...... 120
UDXT> U S6 OX TlCLvQT' O O O O O O OOOOOOOOOOOO O O o o o X^&
". Unit Values of Consumptive Use . „ . » » ...... 132
Units of Applied Water o . • ...... • . . . 138
Water Requirements . . „ . . <> ...... 1^3
Present Water Requirements . «... a ...... ikk
Probable Ultimate Water Requirements ...... 1^5
Future Water Requirements of the City of San Luis Obispo . . . lk$
Monthly Demands for Water ...... 150
Supplemental Water Requirements ...... 152
Present Supplemental Water Requirements ...... 153
Probable Ultimate Supplemental Water Requirements ...... 15^
CHAPTER IV. PLANS FOR WATER SUPPLY DEVELOPMENT 156
Plans for Local Conservation Development ...... 159
Further Development of Ground Water Storage ...... l60
iii 1
Page
Potential Surface Storage Developments .o<.« o 0(. o. 162
Lower Jack Dam and Reservoir <, « n « • « • « . . „ . 172
Santa Rita Dam and Reservoir ».•<>. . . . . « „ . <, 178
San Miguelito Dam and Reservoir O0 o« e 96 <, o«o iQk
Jarrett Shut -In Dam and Reservoir ,o 80 o c.«,ooo 4 191
Bald Top Dam and Reservoir « . „ « . » . <, <, e « o . . 200
Upper Ragged Point Dam and Reservoir . » <. . » » 207
Yellow Hill Dam and Reservoir «. „ e « « » « e «, . . «, * 213
San Simeon Dam and Reservoir ° . « » e • « . . o <> • <, 221
Santa Rosa Dam and Reservoir . > „ „ « „ « . * <, . » » 227
Whale Rock Dam and Reservoir , » . <, o <, <, • « . » <> . 23*+
Lopez Dam and Reservoir . „ «. „ » « . . » . <> « » . . . 242
Alternative Plans for Water Supply Development » «, « . « . . 2^9
Jack Creek and Santa Rita Projects » . • . • « » . « . « . « 25^
Nacimiento Projects ». e ,oo«coor,.ooeo»oc. 255
L"Oasx>aj_ Jrrojecus e©»©«e©a«oooo©©©e©ooooe dip .
Whale Rock Project <> 8 <,»<> . o <, o o » «©...> » n » 26
Organizational and Financial Aspects of Water Resources
Development « e <> 8 <> « <> <> o e <, » e <> <> * <> « <> 263
Plans for Importation of Water . » . . = <, s « <, « . « » . 26>
Featner River Project o«ooo6«o«eooo««ooooo 2o,'
Other Units of the California Aqueduct System • <, • « . 2 68
rJ-OOQ. L'On"trol ooo©oeeoo»t>ooe«>oooooooe€>oo« <— f 2
Upper Salinas River Valley » a • . » a . e » » •> © o • e * ° 27 3
Arroyo Grande Valley «.o©eooe« 8a «o«io©oooeo 27^
Santa Maria River Valley . <> © ooooooooooaooooo
iv Page
CHAPTER V. SUMMARY OF CONCLUSIONS AND RECOMMENDATIONS 282
Summary of Conclusions ...... 282
Recommendations ...... 288 TABLES
Table No . Page
1 Summary of Climatological Data for Selected Stations in San Luis Obispo County and Vicinity ...... 18
2 Population of Incorporated Cities, San Luis Obispo County ...... 22
3 Areas of Hydrologic Units and Subunits ...... 27
k Maximum, Minimum and Mean Seasonal Precipitation at Selected Stations in San Luis Obispo County .... 32
5 Recorded and Estimated Seasonal Precipitation at Selected Stations in San Luis Obispo County and Vicinity ...... 37
6 Mean Monthly Distribution of Precipitation at Paso Robles and San Luis Obispo ...... ^0
7 Stream Gaging Stations in San Luis Obispo County and Vicinity ...... ^3
8 Average Monthly Distribution of Seasonal Natural Runoff of Nacimiento River and Arroyo Grande Creek During Base Period, 1935 -3°" Through 1950-51 ...... kj
9 Estimated Seasonal Natural Runoff in Selected Streams in San Luis Obispo County During Base Period, 1935-36 Through 1950-51 ...... U9
10 Major Exchanges of Water Between Hydrologic Units in San Luis Obispo County ...... 52
11 Summary of Characteristics of Selected Ground Water
Basins in San Luis Obispo County ...... 60
12 Estimated Presently Developed and Maximum Safe Seasonal Yield of Ground Water Supplies in
Portions of San Luis Obispo County and Vicinity . . 6l
13 Mineral Analyses of Surface Waters at Selected Stations in San Luis Obispo County ...... 92
Ik Typical Mineral Analyses of Ground Waters in San Luis Obispo County ...... 95
vi Table No .
15 Historic Diversions and Releases From Salinas
ri6s srvoir 000000000 a o o o o o • 000 o » # jLeLm
16 Organized Water Agencies in San Luis Obispo County,
Xy^lX o o * o • o o 0000c 0000 00 00 © o © * JLX (L
17 Present Water Service Areas in San Luis Obispo County,
X./J J> 0009009000009000 000000^0 JLJ_0
18 Land Classification Standards o <> o » . » » » . » . 122
19 Classification of Irrigable Lands in San Luis Obispo
wO\iriVy" > J.ypti X C. ( i ooooooooooooouoo oooo
20 Probable Ultimate Water Service Areas in San Luis Obispo wOuilujr o#ooo©ooo 90000000*00000 J-^Jl
21 Estimated Unit Values of Mean Seasonal Consumptive Use
of Water in San Luis Obispo County <> . » o <, » <. « 137
22 Measured Average Seasonal Application of Irrigation Water on Representative Crops in San Luis Obispo
wOUil uV ooo»oooooooooo • OOOO 0000 X.J/
23 Estimated Irrigation Efficiencies Under Present and Probable Ultimate Conditions of Development in San Luis Obispo County 00000.000000000 lUl
2k Estimated Mean Seasonal Units of Applied Water in San Luis Obispo County Under Present Conditions of
jJ€V6J_ 0piri6n"C 00*000000 00000 o 00 0000 Xli'L.
25 Estimated Present Mean Seasonal Water Requirements in San Luis Obispo County 000000000000000 lli5
26 Estimated Probable Ultimate Mean Seasonal Water
Requirements in San Luis Obispo County . ° o » IkQ
27 Estimated Average Monthly Distribution of Seasonal
Demand for Water in San Luis Obispo County o o » o 152
28 Estimated Presently Developed and Maximum Practicable Safe Yield of Ground Water Supplies in Portions
of San Luis Obispo County and Vicinity » ° ° . o . • l6l
29 Recorded and Estimated Seasonal Runoff During Base Period at Selected Dam Sites in San Luis Obispo
Coiinty and Vicinity »*,«oo 3 ,>oooooooo. 166
vi 1 Table No. Page
30 Estimated Average Monthly Net Evaporation During Base Period at Selected Reservoir Sites in San Luis Obispo County and Vicinity ...... 168
• ''••.'.«'."'.' 31 Areas and Capacities of Lower Jack Reservoir . 173
32 General Features of Two Sizes of Dam and Reservoir at the Lower Jack Site on Jack Creek ...... 176
33 Areas and Capacities of Santa Rita Reservoir ...... 179
3^ General Features of Two Sizes of Dam and Reservoir at the Santa Rita Site on Santa Rita Creek ...... ~. 182
35 Areas and Capacities of San Miguelito Reservoir ...... 185
36 General Features of Two Sizes of Dam and Reservoir at the San Miguelito Site on Nacimiento River ..... 188
37 Areas and Capacities of Jarrett Shut-in Reservoir .... 193
38 General Features of Three Sizes of Dam and Reservoir
at the Jarrett Shut -In Site on Nacimiento River . . • 196
39 Areas and Capacities of Bald Top Reservoir ...... 202
1+0 General Features of a Dam and Reservoir at the Bald
Top Site on San Carpoforo Creek . . <> ...... 205
1+1 Areas and Capacities of Upper Ragged Point Reservoir . . . 208
1+2 General Features of a Dam and Reservoir at the Upper Ragged Point Site on San Carpoforo Creek ...... 211
1*3 Areas and Capacities of Yellow Hill Reservoir, Upper Site ...... 2ll+
1+1+ Areas and Capacities of Yellow Hill Reservoir,
Lower Site ...... 215
1+5 General Features of Three Sizes of Dam and Reservoir at the Yellow Hill Site on Arroyo de la Cruz .... 2l8
1+6 Areas and Capacities of San Simeon Reservoir ...... 222
1+7 General Features of a Dam and Reservoir at the San Simeon Site on San Simeon Creek ...... 225
viii Table No .
kQ Areas and Capacities of Santa Rosa Reservoir ...... 229
k$ General Features of Three Sizes of Dam and Reservoir
at the Santa Rosa Site on Santa Rosa Creek . . . . 232
50 Areas and Capacities of Whale Rock Reservoir ...... 236
51 General Features of Two Sizes of Dam and Reservoir at the Whale Rock Site on Old Creek ...... 239
52 Areas and Capacities cf Lopez Reservoir ...... 2^4
53 General Features of Two Sizes of Dam and Reservoir at the Lopez Site on Arroyo Grande Creek ..... 2k"J
5^ Comparison of Water Yields and Capital and Annual Costs of Surface Storage Developments in San Luis Obispo
County and Vicinity ...... 252
55 Estimated Capital and Annual Costs of Feather River Project Water Delivered in Cholame Creek in San Luis Obispo County ...... 268
56 Estimated Requirements for Imported Water Supplies in Upper Salinas.. Coastal; Carrizo Plain, and San Joaquin Hydrologic Units Under Ultimate Conditions of Development ...... 272
IX PLATES
(Plates 1-23 are bound at the end of Volume l)
Plate No .
1 Location of San Luis Obispo County
2 Hydrologic Units, 1954
3 Lines of Equal Mean Seasonal Precipitation, 1897-98 to 1946-47
4 Representative Precipitation Characteristics in San Luis Obispo County
5 Stream Gaging and Water Sampling Stations, 1954
6 Representative Runoff Characteristics in San Luis Obispo County
7A Upper Salinas Hydrologic Unit, Areal Geology, 1954
7B Coastal and Santa Maria Hydrologic Units, Areal Geology, 1954
7C Carrizo Plain and Cuyama and San Joaquin Hydrologic Units, Areal Geology, 195*+
8A Geologic Cross Sections, A -A; B-B; C-C* and D-D*
8B Geologic Cross Sections, E-E; F-F; G-G; H-H 1 and J -J 1
9A Upper Salinas Hydrologic Unit, Lines of Equal Elevation of Ground Water, Fall, 1954
9B Coastal and Santa Maria Hydrologic Units, Lines of Equal Elevation of Ground Water, Fall, 1954
9C Cuyama, Carrizo Plain and San Joaquin Hydrologic Units, Lines of Equal Elevation of Ground Water, Fall, 1954
10 Fluctuation of Water Levels at Selected Wells
11A Upper Salinas Hydrologic Unit, Present and Probable Ultimate Land Use, 1953
11B Coastal and Santa Maria Hydrologic Units, Present and Probable Ultimate Land Use, 1953
11C Cuyama, Carrizo Plain and San Joaquin Hydrologic Units, Present and Probable Ultimate Land Use, 1953
12 Monthly Distribution of Mean Seasonal Consumptive Use of Water By Representative Crops, San Luis Obispo County Plate No.
13 Projection of Population and Water Requirement of City of San Luis Obispo
Ik Existing and Potential Water Supply Developments, 195*+
15 Jarrett Shut -In Dam and Saddle Dam on Nacimiento River
16 Lower Jack Dam on Jack Creek
17 Santa Rita Dam in Santa Rita Creek
18 Yellow Hill Dam on Arroyo de la Cruz
19 Whale Rock Dam on Old Creek
20 Lopez Dam on Arroyo Grande Creek
21 Relationship Between Storage Capacity of Reservoirs and Capital Cost
22 Relationship Between Storage Capacity of Reservoirs and Net Safe Seasonal Yield
23 Relationship Between Net Safe Seasonal Yield of Reservoirs and Annual Unit Cost
Plates listed below follow indicated Appendixes in Volume II
Plate No. Appendix
H-l Soil Moisture Depletion and Accretion H
1-1 Major Existing and Proposed Recreational Areas, 1956 I
xi APPENDIXES
(Appendixes are bound in Volume II)
Page
A« Agreement and Its Supplements a Between the State Water Resources Board, the (County of San Luis Obispo,, and the Department of Public Works •«»««»ea*«a A-l
Bo Geology and Ground Water of San Luis Obispo County,
OctJ-XX QX^ni3> O » O B O ® ® OOOOO 9 9 * * 9 o o 9 JD^JL
C« Records of Precipitation in San Luis Obispo County and Vicinity, Not Previously Published „ «••»•••• C-l
D« Records of Daily Runoff and Miscellaneous Stream Flow Measurements in San Luis Obispo County and Vicinity, Not Previously Published » o «»•••• • D*>1
E« Records of Depths to Ground Water at Measurement Wells in San Luis Obispo County and Vicinity »•«»•• E=l
F« Records of Mineral Analyses of Surface and Ground Water Supplies in San Luis Obispo County and
VlCinity oeooo»oo«oe»»o»ooo«»»eeO J? *!
G» Applications to Appropriate Water in San Luis ObiSpO COUnty eOeooOoo»»«oe»»»s« «ec G—l
He Soil Moisture Depletion and Applied Water Studies »•••».> H-l
I. Plans for the Protection and Development of Recreational Resources in San Luis Obispo County • • • 1-1
J. Recorded and Estimated Runoff at Selected Stations in San Luis Obispo County and Vicinity During
16-Year Base Period^ 1935-36 Through 1950*-51 * „ . • • J-l
IV O XleJLQ &OUCll€S 9 9 9 • ft <5 0O 9900090000 09 ft "J.
L« Estimates ox Cost •oa»oo#«a**»°»aa>a«t*> L™=i
Mo Alternative Plan of Development of Nacimiento and San Antonio o Rivers Proposed by San Luis
Obispo County ...... <,»<>..<,...<, M-l
xii :
GOODWIN J. KNIGHT Governor RVEY O. BANKS ADDRESS REPLY TO DlRKCTO* P. O. BOX 38S SACRAMENTO 2 I120 N STREET HI CKORY B-4711
STATE OF CALIFORNIA
SACRAMENTO
May 1, 1958
Honorable Goodwin J. Knight, Governor, and Members of the Legislature of the State of California
Gentlemen
I have the honor to transmit herewith the two -volume Bulletin No. 18 of the State Water Resources Board, entitled "San Luis Obispo County Investigation", as authorized by Chapter 3> Statutes of 1952, as amended.
Work on the San Luis Obispo County Investigation and Bulletin No. 18 was initiated by the Division of Water Resources of the Department of Public Works, under the direction of the State Water Resources Board, and subsequently completed and published by the Department of Water Resources, successor to the foregoing agencies.
Volume I of Bulletin No. 18 contains an inventory of the surface and underground water resources of San Luis Obispo County, estimates of present and probable ultimate supplemental water requirements, and preliminary plans and cost estimates for water development works. Volume II consists of 13 appendixes containing statistical and other data pertinent to the Investigation.
ruly yours, 0. HARVEY 0. /BANKS Director
xiii ACKNOWLEDGMENT
Valuable assistance and data used in this investigation were con- tributed by agencies of the Federal Government, cities, counties, public
districts, and by private companies and individuals <> The Department of Water
Resources gratefully acknowledges this splendid cooperation,,
Special mention is made of the helpful cooperation of the following t
Board of Supervisors, County of San Luis Obispo San Luis Obispo County Surveyor and Road Commissioner San Luis Obispo County Assessor San Luis Obispo County Farm Advisor Monterey County Flood Control and Water Conservation District Board of Directors, Arroyo Grande Soil Conservation District Board of Directors, Upper Salinas Soil Conservation District California State Division of Highways California State Department of Fish and Game United States Agricultural Research Service United States Bureau of Reclamation United States Forest Service United States Geological Survey, Surface Water Branch United States* Soil Conservation Service Pacific Gas and Electric Company
xiv ORGANIZATION
CALIFORNIA WATER COMMISSION
Clair Ac Hill 5 Chairman 9 Redding
A. Frew^ Vice Chairman^ King City-
John P. Bunker,, Gustine Wo P„ Rich, Marysville
Everett L. Grubby Elsinore Phil D. Swinge, San Diego
Kenneth Q, Volk 5 Los Angeles
George Bo Gle&son Chief Engineer
William M. Carah Executive Secretary
xv —
ORGANIZATION
STATE DEPARTMENT OF WATER RESOURCES
Harvey <, Banks . e » o • • • » • . Director of Water Resources
Mojo Shelton . c <> « • « o c Deputy Director of Water Resources
William L« Berry „ o * „ . Chiefs Division of Resources Planning
SOUTHERN CALIFORNIA DISTRICT
Max Bookman o o © © © © © o © o 9 P © 9 © © District Engineer
This investigation was conducted and bulletin prepared under the direction of
Robert Mo Edmonston . Principal Hydraulic Engineer
Lucian J. Meyers • Supervising Hydraulic Engineer
by
Robert H* Born * . Associate Hydraulic Engineer
Paul £. Hood . . Associate Hydraulic Engineer Arnold F. Nicolaus Associate Hydraulic Engineer
Robert G. Thomas , Associate Engineering Geologist
Assisted by
J. w. Shannon <> • o • o • Supervisor, Land and Water Use Section
N. Do Sturm e e e • * * s • © © o o . * Supervising Economist
Ro N. Haley • » . © © 9 Senior Land and Water Use Analyst
C o R. McClure » . © © e « . . Senior Engineering Geologist
Ro F. Claws on • . o © © B © • 9 Associate Hydraulic Engineer
J. 0. McClurg . c e o • • » o Associate Hydraulic Engineer
H. Jo Hanson o . O © * • © • » O • Associate Civil Engineer
Dc E» Eason • • • • © o 9 o Civil Engineering Associate
Jo E o Blakemore « « • • O 9 © * Assistant Hydraulic Engineer
Ro Bo Gunderson • e 9 © 9 • o • Assistant Hydraulic Engineer
W. Vo York a e o © e © . . . Assistant Hydraulic Engineer
C o Ro Hotchkiss » • © © a . . Assistant Engineering Geologist
R. E. Merrill » • « © * o Assistant Land and Water Use Analyst
To Do Harrington a o o 6 © © © . Engineering Aid II
Ho P Hopkins • <> o 9 © 9 © ao©eo« Engineering Aid II
E o E o Schulten « e O • t • © * Junior Engineering Aid
Ho P Zablodil »« © o I * * © • © • o . . • Senior Delineator
Eo Angus • a s • • © © © 9 0*0 • © • © Delineator
T. Wo Matthews . •> © • • O 9 ©•«•©© Delineator
.0—
Paul L. Barnes, Chief, Division of Administration
Isabel Co Nessler, Coordinator of Reports xid ORGANIZATIONAL CHANGES
This investigation was commenced under the direction of the State
Water Resources Boarde Members of the Board at the inception of the investi- gation included Mr» C„ A<> Griffith*, Chairman^ and Messrs o H« F<, Cozzens,
B» A, Etcheverry*, Clair Hill, R V<, Meikle, Royal Miller, and Phil D„ Swings
At the time this investigation commenced, Mr Q A„ D, Edmonston was
State Engineer and Chief of the Division of Water ResourceSo On November 1 5
1955, Mr« Edmonston retired from State service and was succeeded by
Mr Harvey 0„ Banks, who served in the capacity as State Engineer until his appointment as Director of Water Resources on July 5, 1956<>
The function under which this investigation was conducted was
directed by Mr« T. B 8 Waddell until his retirement from State service on
November 1, 1955, at which time he was succeeded by Mr c W 8 L, Berry<> Mr Berry served as Assistant State Engineer until his appointment as Chief, Division of Resources Planning, on July 5, 1956©
This investigation was under the codirection of Mr T„ M„ Stetson,
Supervising Hydraulic Engineer, from March 1, 195H? until July 1, 1955, at which time he was succeeded by Mr,, L„ Jo Meyerso
# Deceased.
xvii OHGANIZATION
COUNTY OF SAN LUIS OBISPO
BOARD OF SUPERVISORS
Dan Fo Sheeny, Chairman, Nipomo
Paul E. Andrew, Cayucos John B„ Ruskovich, Atascadero
M. Roland Gates, Paso Robles Fred C. Kimball, San Luis Obispo
XV3.11 SAN LUIS OBISPO COUNTY INVESTIGATION
CHAPTER I. INTRODUCTION
During the past decade, San Luis Obispo County, like most other counties in California, has experienced an increase in population concur- rently with an expansion and intensification of irrigated agriculture. This growth, however, has not been of equal magnitude with the phenomenal increases of population, industry, and agriculture experienced in other areas of the
State such as the Los Angeles, San Francisco, and San Diego metropolitan areas
and the Sacramento and San Joaquin Valley agricultural areas . The unprece- dented development of these latter areas, with the attendant serious problems of water supply, illustrates the potential problems which will arise in San
Luis Obispo County in the future* Recent growth of population and agriculture within the County has resulted in an increased demand on both surface and
underground water resources . In some areas of the County, a shortage of irrigation water prevails during the latter part of the irrigation season.
Increasing development of urban and domes tic use of water within the Cities of San Luis Obispo, Paso Robles, and other communities indicates that, within the near future, available water supply sources may be inadequate to meet the increased demand*
A lesser water problem in San Luis Obispo County is that of flood control. Flood waters have caused damage to lands adjacent to the lower reaches of Arroyo Orande Creek and the Santa Maria River* Recent reclamation
-1- •
of lands adjacent to these streams and intensification of agricultural prac- tices hsrtre increased the potential flood damage in these areas
The growth of population and industry in San Luis Obispo County in the future, together with the anticipated increase in irrigated agriculture, will require an extensive program of local development of both surface and underground water resources; and full satisfaction of the ultimate water-using potential within the County will require importation of substantial amounts of water from sources outside of the County.
Authorization for Investigation
Concern over the adequacy of available water supplies for present and future requirements of San Luis Obispo County prompted the Board of
Supervisors of the County, the County Water Resources Committee, and the
County's legislative representatives to request the California Legislature to
provide funds for a water resources investigation of the County • As a result, the Legislature, in Assembly Bill No. 1, Chapter 3> Statutes of 1952, Item
268.5(b), made an appropriation of the sum of $20^000 for a comprehensive survey of the water resources of the County. The State Water Resources Board, at its meeting of June 6, 1952, directed the State Engineer to submit to the
Board a proposed work program to carry out the surveys. On July 18, 1952, the
State Water Resources Board approved a recommendation of the State Engineer for a three-year comprehensive survey of the water resources of San Luis
Obispo County.
Objectives of the investigation were to include determination of the nature and amount of local water resources, present and probable ultimate water requirements, present and probable ultimate supplemental water require- ments, and the development of preliminary plans to meet those supplemental
-2- o >
requirements from local or imported sources. It was also considered that the
investigation should involve determination of flood control requirements and
include preliminary plans for protective works if required . It was proposed,
that a report covering the investigation would be submitted to the Board on
June 30, 1955^ or as soon thereafter as possible*
Continuation of the San Luis Obispo County Investigation for the second year was authorized under terms of an agreement dated July 1, 1953
between the State ¥ater Resources Board , the County of San Luis Obispo , and the State Department of Public Works acting through the agency of the State
Engineer
The agreement provided that the sum of $30,000 would be expended during Fiscal Year 1953-5U and that an additional $26,000 would be expended during Fiscal Year 195^-55 to complete the work program of the three-year comprehensive survey. Of the $56,000 so expended, $28,000 was provided by the
State Water Eesources Board and an equal amount was provided by the County of
San Luis Obispo • A supplemental agreement executed by the same parties on
July 1, 195^5 authorized funds to complete the investigation and report during
Fiscal Year 1955" Funds authorized under the latter agreement were exhausted prior to completion of the report and a second supplemental cooperative agree- ment authorizing the expenditure of $5^000 to complete the report was executed by the afore-mentioned parties effective May 1, 1956» Work on the report subsequent to July h, 1956, was accomplished by personnel of the State
Department of Water Eesources, successor to the State Water Resources Board
and Division of Water Resources c
The following tabulation presents the cost of the investigation by years, the respective shares of the State of California, and the County of
San Luis Obispo, a ad the total costo State of County of Annual California San Luis Obispo total
1952-53 $20,000 $™ $20,000
19$>$l 15,000 15,000 30,000
195^55 13,000 13,000 26,000
1955-56 2,500 2,500 5^000*
TOTALS $50,500 $30,500 $81,000
•wFunds available for expenditure during Fiscal Year 1956-57*
Additional funds have been expended in San Luis Obispo County by the
State Water Resources Board in connection with the State-Wide Water Resources
Investigation, authorized by Chapter I51jl, Statutes of 19h7 3 and by the State
Division of Water Resources for studies of quality of water pursuant to
Sections 229 and 230, Division 1, of the California Water Code. Results of these investigations have been used in connection with the San Luis Obispo
County Investigation.
Copies of the agreements between the State Water Resources Board, the County of San Luis Obispo, and the Department of Public Works are included as Appendix A.
Related Investigations and Reports
The following reports of prior investigations, concerning various phases of water resources problems of San Luis Obispo County, were reviewed in connection with the current investigation.
Adams on, Paul L. , Jenks, Harry N., and Jenks, John H. "Report on Water and Sewage Systems for City of San Luis Obispo". September, 1951i»
Arroyo Grande Soil Conservation District and San Luis Obispo County Flood
Control and Water Conservation District, in cooperation with U» S «. Forest Service and Soil Conservation Service. "Watershed Work Plan, Arroyo Grande Creek Watershed, San Luis Obispo County, California". October, 1955°
t -a- . . • o .
California State Department of Public Works, Division of Water Resources,
"Salinas Basin Preliminary Investigation" c 1933
California State Department of Public Works, Division of Water Resources, "Salinas Basin Investigation". Bulletin Nos. 52, J>2-A, 52 ~B. July, 19li6
California State Department of Public Works, Division of Water Resources "Salinas Reservoir System in San Luis Obispo County., California". March, 19k? <
California State Department of Public Works, Division of Water Resources c "Survey of Petroleum Industry Waste Disposal Practices, Arroyo Grande Oil Field, San Luis Obispo County". August, 1953°
California State Department of Public Works, Division of Water Rights. "Investigation of Lopez Creek as a Source of Water Supply for the
City of San Luis Obispo, Applications 3^8 and 1990" . December 1, 1921,
Hamlin., Homer. "Water Resources of the Salinas Valley". United States Geological Survey Water-Supply and Irrigation Paper No. 89. 190li.
Harding, S. T. and Kempkey, A. "Water Supply of the Salinas Valley and Storage Projects for Its Additional Use". January 10, 1955°
Harding, So To and Kempkey, A. "Water Supply of the Salinas Valley and Storage Projects for Its Additional Use - Supporting Material" October^ 1953
Macabee, L. Cedrice "Report on Atascadero Water Works, San Luis Obispo County, California". March, 1952.
Marliave, Chester. "Geological Report on El Nacimiento Dam Site Situated Across El Nacimiento Branch of the Salinas River in San Luis Obispo County, California". June 2, 19i|lc
Ramseier, Roy Ed-win,, "Additional Water Sources for the City of El Paso de Robles". July $, 1951°
United States Army, Corps of Engineers. "Interim Flood Control Survey Report, Salinas River, California". I9I4O.
United States Army, Corps of Engineers. "Survey, Flood Control, Arroyo Grande Creek, San Luis Obispo County, California". March, 19142.
United States Army, Corps of Engineers, "Report on Survey, Flood Control,
Santa Maria River and Tributaries, California" June 15 , 1953°
United States Army, Corps of Engineers. "Survey Report, Salinas River 9 California, for Flood Control and Allied Purposes". 1953° Unpublished
United States Department of Agriculture, Bureau of Chemistry and Soils, "Soil Survey of the Paso Robles Area, California". 1928.
-5- „ «
United States Department of Agriculture , Bureau of Chemistry and Soils,,
"Soil Survey of the San Luis Obispo Area, California". 1928 „
United States Department of Agriculture, Bureau of Soils o "Soil Survey of the Santa Maria Area"* 19l6o
United States Department of Agriculture,, Forest Service and Soil Conser- vation Service* "Reconnaissance Sedimentation Survey, Salinas Reservoir, San Luis Obispo County, California",, September, 1953<>
United States Department of Interior, Bureau of Reclamation . "Santa
19 Maria Project, Southern Pacific Basin, California . June, 1951°
United States Department of Interior 5 Geological Survey* "Geology and Ground Water Resources of the Santa Maria Valley Area, California"
Water Supply Paper 1000 . 1951,
United States Department of Interior 9 Geological Survey,, "Ground Water in the Cuyaraa Valley, California 8 ^ Water Supply Paper 1110-Bo 1951
The Division of Water Resources recently completed surveys and studies for the State-Wide Water Resources Investigation, authorized by
Chapter i5iil. Statutes of 19k?o This investigation, under the direction of the State Water Resources Board., bad as its objective the formulation of The
California Water Plan for full conservation, control, and utilization of the
State's water resources to meet present and future water needs for all bene- ficial purposes and uses in all parts of the State insofar as practicable,)
The results of this comprehensive investigation are reported on in three publications of the State Water Resources Boardo
The first of these publications. Bulletin No* 1, contains an inven- tory of the available surface water supplies of the State and was published in final form under the title, "Water Resources of California", dated 1951° The second publication, Bulletin No» 2, entitled "Water Utilization and Requirements in California", dated June, 1955/. contains estimates of present and probable ultimate land use and water requirements of the State* Data compiled in these two publications, pertaining to San Luis Obispo County, have been used in the preparation of this report., The third in the foregoing series of publications,
-6- which sets forth a comprehensive plan for the development and utilization
the water resources of the State, was published in May, 1957.? as Bulletin
No. 3.0 entitled "The California Water Plan". Plans for water resource
developments presented in this report on the San Luis Obispo Investigation
have been developed in conformity with standards and objectives established
for the afore-mentioned California Water Plan and have been incorporated into
the over- all plan.
By direction of the State Water Resources Boards the Division of
Water Resources prepared plans for the Feather River Project as the initial
unit of The California Water Piano A report on this initial unit entitled
"Report on Feasibility of Feather River Project and Sacramento=San Joaquin
Delta Diversion Projects Proposed as Features of The California Water Plan",
dated May 5 1951 $ was submitted by the Water Resources Board to the California
Legislature of 1951° The proposed features were authorized by the Legislature
for construction by the Water Project Authority of California in Chapter 11*11 ^
Statutes of 1951 s and subsequently funds in the amount of $2 5 227 3 056 were
appropriated by the Legislature for additional studies and investigations of
the project during Fiscal Years 1953 5 195kj and 1955 » A report on these
additional studies and investigations , entitled "Program for Financing and
Constructing the Feather River Project as the Initial Unit of The California
Water Plan",, dated February, 1955$ was completed and transmitted to the
Legislature of 1955 by the Water Project Authority.
The Feather River Project features have for their purpose the
exportation of surplus waters of the Feather River and of the Sacramento^
San Joaquin Drainage Basin to southern portions of the State to provide supplemental water supplies to the west side of the San Joaquin Valley, the
South San Francisco Bay area, and the southern California area. Plans for
importation of ^supplemental water supplies to San Luis Obispo County from the
Feather River Project were studied and the results of these studies are presented in this bulletin.,
Additional funds in the amount of $1, 773,000 were appropriated by the
Legislature in its Budget Acts of 1956 and 1957 for studies of alternative routes for the Feather River aqueduct Results of these current studies could not be included in this bulletin as they are scheduled for completion in the
spring of 1958 «>
An investigation of the water resources of the Salinas Basin was completed in 1955 by the Division of Water Resources under a cooperative agreement between the State Water Resources Board, the Monterey County Flood
Control and Water Conservation District, and the Department of Public Works acting through the agency of the State Engineer. A report upon the findings of the investigation is being prepared in preliminary form under the title
89 "Bulletin No. 19 a Salinas River Basin Investigation ,, Basic data and plans of development compiled for the Upper Salinas River Basin in connection with the
San Luis Obispo County Investigation were utilized in the preparation of the
af ore-mentioned report on the Salinas River Basin c
Results of the San Luis Obispo County Investigation were published in summary form by the State Water Resources Board in a report entitled
"Interim Summary Report on San Luis Obispo County Investigation", dated
October, 1955° & summary of conclusions drawn from the current investigation
was presented in the afore -mentioned report <>
Scope of Investigation and Report
Enabling legislation for the investigation authorized a comprehen-
sive survey of the water resources of San Luis Obispo County <, The objectives -8- • •
of the investigation were defined in the work program approved by the State
Water Resources Board and an outline of the work required to accomplish thcjt objectives was contained in the initial agreement between the State Water
Resources Board, the County of San Luis Obispo, and the Department of Public
Works. Achievement of these objectives necessitated evaluation of surface and underground water supplies and the determination of present and probable ultimate land use and water utilization and requirements* Field work and office studies in the investigational area commenced in July, 1952, and continued into June, 1955
During the course of the field investigation, basic hydrologic data in the form of precipitation and stream flow records? as well as records of ground water levels at wells, were obtained in the field by the Division of
Water Resources or were compiled from records of public and private agencies.
Precipitation records were obtained for I46 stations maintained by the U. S. Weather Bureau and 95 stations maintained by local private and public entities
Stream flow records were obtained from 15 gaging stations maintained by the U. S. Geological Survey. Four additional stream gaging stations equipped with automatic water stage recorders were installed and maintained by the Division of Water Resources During the course of the investigation, three additional stream gaging stations equipped with automatic water stage recorders were installed^ In addition, 17 stations equipped with nonrecording staff gages or datum reference points were established and maintained for varying periods of time on streams throughout the County. Frequent stream flow discharge measurements were made along Salinas River and Arroyo Grande
Creek, and their tributaries, for gaging station rating purposes and to determine stream characteristics during periods of influent and effluent flow
-9- o „
for underlying ground water basins*
A field survey was made for the purpose of determining the location, type^ and characteristics of operating and nonoperating irrigation, municipal, and industrial water wells in the County. During the investigation, approxi- mately 1,300 wells were located in the field in addition to some 70 wells previously located by the U» S. Geological Survey in the Cuyama and Santa
Maria Units o Fall and spring measurements were made at about hlO wells chosen to form a comprehensive measuring grid over ground water basins identified
within the County o In addition, the U* S. Geological Survey reports measure- ments made at 11 wells in the Cuyama and Santa Maria areas each fall and spring as part of its continuing investigation. Measurements were made to determine monthly fluctuations of water levels at approximately 70 key wells
for varying periods of time throughout the investigational seasons . Water stage recorders were maintained for varying periods of time on a total of 25 nonoperating or abandoned wells throughout the County for the purpose of securing short-term continuous records of ground water level fluctuations
Geologic features of ground water basins underlying the area were investigated, including occurrence and movement of ground waters and available storage capacities therein This study included the collection and analysis of approximately 300 water well logs and 150 oil well or shot hole logs.
Geologic data collected by the U. S. Geological Survey in connection with the continuing investigation of ground water conditions in Cuyama and Santa Maria
Valleys by that agency in cooperation with Santa Barbara County were also utilized. The report on the geologic investigation is presented in Appendix B of this report
Available historical hydrologic data and geologic information for the ground water basins in the County were found to be inadequate to make
-10- preliminary determinations of ultimate safe yields of these basins*
Studies were made of the mineral quality of surface and underground
waters in order to evaluate their suitability for beneficial use and to
determine the extent and cause of any degradation thereofo To supplement
available data of this nature, 111* complete analyses of surface waters and
160 complete analyses of ground waters were made during the course of the
investigation. Detailed results of available mineral analyses of surface and underground water supplies of San Luis Obispo .County are presented in
Appendix F.
The nature and extent of present land use throughout the County were determined from a detailed survey conducted during 1953" Three supple- mental surveys of selected truck-cropped areas were conducted during 195^> at
three to four-month intervals, following the original survey in order to
evaluate the effects of double and triple cropping* Present water requirements were determined by application of appropriate unit values of water use to the
areas of irrigated lands. Studies were also made of present use of water for urban and suburban areas within the County*
For the prupose of estimating probable future water requirements, a land classification survey was conducted during 195h> Basic criteria were set up to determine the suitability of all nonurban lands for irrigated agricul~ ture. Consideration was also given to the development of nonirrigable lands to an urban and suburban type of use. Appropriate unit values of water use were applied to the probable ultimate pattern of land use to obtain the
estimated ultimate water requirements of the County e
Future requirements for municipal water supplies were estimated from projections of population and per capita water consumption data based upon development of areas of the State with characteristics similar to the investi- gational area. -11- »
In order to develop basic information on consumptive use of water
by irrigated and nonirrigated crops in the investigational area, as well as
verifying corresponding values estimated for other nearby climatically similar
areas, studies were made of soil moisture depletion at representative plots of
irrigated and nonirrigated agriculture during the 1953 irrigation season
Consumptive use studies of nonirrigated agriculture and also of native vegeta-
tion were continued into 195he A total of 17 plots of irrigated agriculture and
seven plots of nonirrigated agriculture and native vegetation were studiede
In addition to the studies of soil moisture depletion, current irrigation practices in San Luis Obispo County were surveyed in order to
determine unit values of water application to important crops on lands having
various soil types during the 19Sh irrigation season <. Records of water well
production^ acreage served, crops irrigated,, number and period of irrigations^ and the amounts of water applied were compiled.. This information was compiled with the aid of records of power consumption by irrigation pumps and results
> of pump operation tests furnished by the Pacific Gas and Electric Company
Detailed results of soil moisture depletion and applied water studies are presented in Appendix Ho
Hydrologic studies were made for each pf the major stream systems©
These studies included determination of presently developed safe yield of
surface and underground water supplies, present and probable future supple- mental water requirements, present waste to the ocean from major streams, and
the portion of this waste susceptible of conservation by both surface and underground reservoirs.
The development of possible plans for additional conservation of
local surface water supplies included field examination of feasible dam sites.,
together with geologic investigations thereof 8 Preliminary designs and
-12- estimates of cost were prepared for several heights of dams at many of the sites, and of water conveyance systems and appurtenant works* Preliminary plans and estimates of cost were also prepared for works necessary to import supplemental water from the main aqueduct of the authorized Feather River
Project. Consideration was also given to the financial and organizational aspects attendant upon the development of local and imported water supplies.
Detailed estimates of runoff at various dam sites, reservoir yield studies, and estimates of cost of various projects considered are presented in
Appendixes J, K, and L, respectively* Study was also made of fish, wildlife, and recreational aspects of proposed water supply developments for the County*
A report on this study is presented in this Bulletin as Appendix I.
Results of the San Luis Obispo County Investigation are presented in this report in the four ensuing chapters* Chapter II, "Water Supply", contains evaluations of precipitation and stream flow. It also includes results of investigation and study of underground hydrology, and sets forth estimates of presently developed safe yield of surface and underground water supplies* Data regarding the mineral quality of surface and underground water supplies are also presented therein* Chapter III, "Water Utilization and Requirements", includes results of determinations of present and probable ultimate land use and water requirements, and contains estimates of present and probable ultimate supplemental water requirements. It also includes available data on demands for water with respect to rate, time, and place of delivery. Chapter IV, "Plans for Water Development", describes preliminary plans for conservation and utilization of local water supplies, including operation and yield studies, design considerations and criteria, estimates of cost for the construction of works, and analyses of the financial and organiza- tional aspects thereof. Similar consideration is given to the development of
=13- imported water supplies.. It also includes the results of evaluation of prior
reports and investigations on flood control aspects . Chapter V, "Summary of
Conclusions and Recommendations", includes conclusions and recommendations resulting from the investigation and studies.
Area Under Investigation
The area 'under investigation comprises all the lands of San Luis
Obispo County. For purposes of analysis of available water supply , it was found necessary in some instances to also investigate portions of adjacent counties containing drainage areas tributary to San Luis Obispo County.
San Luis Obispo County is situated In the Central Coastal Area of
California about midway between the Cities of San Francisco and Los Angeles.
The County adjoins Santa Barbara County on the south, Kern County on the east,
Monterey County on the north, and the Pacific Ocean on the vest. San Luis
Obispo County has an average dimension of about 60 miles both north and south
and east and west, with an area of 3*326 square miles c The location of the
County is shown on Plate lj, "Location of San Luis Obispo County".
San Luis Obispo County is traversed by five segments of mountain ranges comprising the South Coastal Geomorphic Province. In order of importance, they include the Santa Lucia, Temblor, La Panza, Caliente, and
San Luis Ranges. These ranges, which trend generally in a northwest to south- east direction, separate the County into five fairly distinct drainage areas: the Salinas River Basin, which drains in a northwesterly direction to the
Pacific Oceanj the Carrizo Plain, which is an enclosed basin; the coastal drainage area, which is tributary to the Pacific Ocean between Monterey County
-14- on the north and Santa Maria River Basin on the south j the Santa Maria River
Basin comprising portions of the drainage areas of the Santa Maria and Cuyama
Rivers j and the San Joaquin Valley drainage area, which is tributary to Tulare
Lake Basin in the San Joaquin Valley e
The drainage area of the Salinas River is l^UOl square miles, of which per or square miles lies within 35 cent l,ShS San Luis Obispo County «,
The headwaters of Salinas River, the largest coastal stream in California south of San Francisco Bay, are located in San Luis Obispo County . About 53 per cent of the area of San Luis Obispo County lies within the Salinas River drainage basin. This portion of the County is characterized by extensive areas of rolling topography with large acreages being suitable for the culti- vation and irrigation of a variety of agricultural crops. Elevations range from about 1*60 feet above sea level in the bed of the Salinas River at the
Monterey County line to h 9 0%U feet at McChesney Mountain in the La Panza
Rangee Several peaks in the Santa Lucia Range, which separates the Salinas
River and coastal drainage areas, attain elevations in excess of 3*000 feet,
the highest of which is Pine Mountain with an elevation of J> s S9h feet„ The
Temblor Range, which parallels the San Andreas fault, forms the divide between the upper Salinas River Basin and the San Joaquin Valley.,
Principal sources of surface runoff tributary to the Salinas River are streams draining the easterly slopes of the Santa Lucia Range, of which the Nacimiento River is the largest. Estrella Creek and its two principal tributaries, Cholame and San Juan Creeks, drain the easterly portion of the
upper Salinas River drainage area c
The Carrizo Plain is a large enclosed basin located in the south- easterly portion of San Luis Obispo County. Small portions of the drainage area tributary to this basin extend into Kern County. The area of the entire
=15» Carri&o Plain watershed is kkl square miles, of which k23 square miles are
Tsoithin San Luis Obispo County. The Carrizo Plain is separated topographically from Salinas River Basin by a low drainage divide between the Temblor and
La Panza Ranges. The Caliente Range forms the drainage divide between the southerly portion of Carrizo Plain and Cuyama Valley,, The Carrizo Plain drainage area varies in elevation from about 1,900 feet above sea level at
Soda Lake near the center of the basin to 5 S Q9% feet at Caliente Mountain.
The floor of the basin averages about 2,000 feet above sea level.
The coastal drainage area includes all watersheds tributary to the
Pacific Ocean from the northerly extremity of San Luis Obispo County to, but not including, Santa Maria River at the southerly extremity of the County.
This coastal drainage area comprises 788 square miles, of which 15 square miles of the San Carpoforo Creek drainage area are located in Monterey County,
The major streams included;, in addition to San Carpoforo Creek, are Arroyo de la Cruz, San Simeon Creek, Santa Rosa Creek, Old Creek, San Luis Obispo
Creek, and Arroyo Grande Creekc These streams drain the westerly slopes of the Santa Lucia Range. The drainage areas of the streams from Morro Bay north produce a large amount of runoff in proportion to their size as compared with drainage areas elsewhere in the County.
Santa Maria River, together with its two major tributaries, the
Cuyama and Sisquoc Rivers, drains an area of 1,881 square miles, about $0% square miles of which are within San Luis Obispo County. The La Panza and
Caliente Ranges separate the Santa Maria River watershed from the Salinas
River watershed and Carrizo Plain, respectively. The floor of Cuyama Valley ranges in elevation between 1,900 feet and 2,900 feet above sea level, averaging about 2,300 feet. The Santa Maria Valley floor varies in elevation from sea level to about 300 feet above sea level.
-16- « „ o
Climate
San Luis Obispo County exhibits a distinct variation in climate
between its coastal and inland sections . The climate in the inland area is
characterized by warm, dry summers and relatively cool, wet winters. During the winter season, temperatures below freezing are common but the long, dry summers provide adequate growing season for a wide range of agricultural production.)
The Carrizo Plain and Cuyama Valley are, to some extent, exceptions in that their high altitudes result in shorter growing seasons limiting the types of agricultural practice. In the inland area, more than 80 per cent of the annual precipitation occurs during the months from December through March.
Most of the precipitation falls as rain with small amounts of snow occurring at the high altitudes on infrequent occasions
The climate in the coastal area of the County is characterized by long, dry, warm summer seasons with frequent ocean fogs, followed by a shorter
wet winter period accompanied by cooler temperatures . The distribution of precipitation is similar in the inland region. In the Lower Arroyo Grande and
Santa Maria Valleys, killing frosts are rare, making possible the practice of double and triple cropping of lands
San Luis Obispo County lies in the path of storms originating off the Aleutian Islands which periodically sweep inland along the Pacific Coast
during the winter seasons . The mountains of the Santa Lucia Range affect the distribution of precipitation by causing major storms to deposit substantially heavier rainfall in the coastal area and over the westerly portion of the
Upper Salinas River Basin than in the easterly portion of the County
Pertinent clima to logical data are presented in Table 1 for five selected stations in San Luis Obispo County and vicinity.
-17- ,
TABLE 1
SUMMARY OF CLIMATOLOGICAL DATA FOR SELECTED STATIONS IN SAN LUIS OBISPO COUNTY AND VICINITY
o o • s Recorded temperature o • Average
^Elevation, s in degrees F. sMean seasonal? number of
Station s in feet o o o sprecipitations days between
sMaximumsMinimumsAverage s in inches ; killing frosts
San Luis Obispo 300 110 20 58.7 21.68 315
Point Piedras Blancas 57 85 31 53.1* 18.31* 351*
Santa Maria 217 101; 22 57 cl H*.22* 351
Paso Robles 71*0 117 58.5 15.82 20U
Guyama 2 5 2i|0 109 8 56,2 5o91 178
Geologv
Geologic formations in San Luis Obispo County have been divided, for the purposes of this investigation, into water-bearing and nonwater-bearing
groups o Nonwater-bearing rocks include pre-Cretaceous granite rocks , marine and nonmarine sediments of Jurassic through Pliocene age, and volcanic rocks of Miocene age. Rocks classified as nonwater-bearing generally yield negli- gible quantities of water to wells and usually contain water of poor quality at depth©
Water-bearing sediments consist of nonmarine sand, gravel, silt, and clay of Pleistocene and Recent ageso The Paso Robles formation and Recent alluvium generally are the most important water-bearing sediments,, The Paso
Robles formation consists of folded and faulted nonmarine sand, gravel, clay, and minor calcareous beds. While reaching an estimated thickness of 3*000 feet in the higher portions of upper Salinas River drainage area, the
•18" o • o
Paso Robles formation is only 200 to IjOO feet thick in the San Luis Obispo
and Arroyo Grande areas . Alluvium underlies the larger valley floors of the
County* In the valley floor of Salinas River, alluvium averages about 30 feet in thickness o In the coastal drainage area, alluvium varies from 60 to 200 feet in thickness and is found only in the larger valleys. Other water-bearing formations are sand dunes and stream deposits of upper Pleistocene age in the
Morro Bay and Arroyo Grande areas. Water°bearing formations yield up to 3.9OOO gallons per minute to wells, with alluvium generally yielding more than older formations
Soils
Soils of San Luis Obispo County vary in their physical and chemical properties in accordance with difference in parent material, method of formation or deposition., and age or degree of development since their
deposition. The soils may be divided into three broad groups 5 (1) residual soils, (2) older valley filling soils,, and (3) Recent alluvial soils
Residual soils include those which have been developed in place on consolidated bedrock of sedimentary, igneous, and metamorphic origin. Soils in this category are found throughout the County on steeper slopes where drainage is generally good and soils are usually shallow and of medium texture
Rock outcrops are frequently found . Moisture holding capacities are rated as fair to good although, because of unfavorable topography or shallow depths,, only a small percentage of soils in this category are suitable for cropping purposes
Older valley filling soils, which comprise a significant proportion of the Upper Salinas River drainage area and are found to a lesser extent in the
San Luis Obispo-Arroyo Grande area, generally occupy intermediate elevations
-19- between residual soils and Recent alluvial soils o Since their deposition, soils of this group have been elevated and later eroded in varying degrees by streams cutting through theim As a result , rolling topography characterizes the areas in which these soils occur o Textures vary from light to medium at the surface to heavy at depth,, Surface drainage is therefore good, but subsurface drainage is often retarded by the heavier subsoils The most highly developed profiles in the County exist in soils of this group*
Moisture holding capacities are fair to good in the upper zones and poor in the lower zones* Failures of shallow rooted, dry»farmed crops on these soils
have been reported in years of deficient rainfall « Soils with the most highly developed profiles are fertilized as standard cropping practiceo A wide range
of climatically suited crops may be grown on older valley filling soils a
Recent alluvial soils usually occupy flood plains adjacent to stream channels and alluvial fans where accretions and depletions of soil material occur each year* Because this soil is in the process of accumulation, profiles are, at best, in the early stages of development.. Soil depths vary considerably, often exceeding six feetc Textures vary from light to medium in the upper Salinas and Carrizo Plain drainage areas with stratified sands and gravels often found beneath the surfaceo Heavier textures are found in some soils along the coasto Drainage is usually good in the lighter textured soils except during periods of inundation* In the case of heavier soils, perched water is often found, especially above stratified clays. With proper applica- tion of water and careful use of commercial fertilizers where required, Recent alluvial soils have a high agricultural value
20» Present Development
Development of San Luis Obispo County began with the establishment
of its two missions, San Luis Obispo de Tolosa in 1772, around which grew the
City of San Luis Obispo and San Miguel Archangel in 177li* at the site of the
present community of San Miguel. Early life was centered about the missions
where the raising of cattle and grain was the chief occupation- It was not
until the latter half of the 19th Century that any appreciable growth in
population or agricultural development occurred.
At the time of its formation in 1850 as one of the original 27
counties of the State, the entire population of San Luis Obispo County was listed as 336, exclusive of Indians- By 1890, the first year for which federal census figures were compiled, the population of the County was reported as 16,072, an increase of ljOO persons per year. In 1930, the popula-
tion has increased to 29,613, an average increase of about 300 per year, and in 1950, the population of the County was listed as 5l>Ul7, an average increase of more than 1,000 per year. The population of the County was estimated by the State Department of Finance to be 60,800 on July 1, 195$, which represents an increase since the 1950 census of more than 1,800 per year.
The foregoing population growth figures, while relatively small in actual numbers as compared with other parts of the State, indicate a trend of population growth, with attendant general expansion, which may be expected to
assume sizable proportions in the future e
For comparative purposes, available federal census figures for incorporated cities in San Luis Obispo County are listed in Table 2 for each census since 1930, and for the most recent special census.
21- TABLE 2
POPULATION OF INCORPORATED CITIES, SAN LUIS OBISPO COUNTY
Tppulation City 19iiO s"~1950~
San Luis Obispo 8,276 8 ; 881 1^180 17,229 (1955) Paso Robles 2,573 3,0145 M35 6,1148 (1952) Arroyo Grande 892 1,090 1,723 2,061 (1953) Pisrao Beach No data 1,292 1,1*25 1,921* (1953)
Agricultural development in San Luis Obispo County began with the first plantings of corn at Mission San Miguel in 1797= Later barley and wheat were planted there as well as at Mission San Luis Obispo The first irriga- tion system in California was reported to have been built at Mission San
Miguel where irrigation water was diverted by ditch from Santa Ysabel Springs,
15 miles south of the missiono Prior to the l870 e s barley was the principal
crop grown o In 1868 interest was aroused in the production of wheat and by
1873 i approximately 5,000 acres were sown. In 1915, one of the peak years,
353 36OO acres of wheat were reported to have been sown.. The County Agricul- tural Commissioner reported 91,700 acres in wheat, 67,300 acres in barley, and
5,100 acres in oats for the year 1955c
The extensive areas of the Upper Salinas Valley and Carrizo Plain within San Luis Obispo County contain about 1^,260,000 acres of valley and hill
lands o Because of rolling topography which characterizes the area, agricultural development until recent times has been chiefly limited to cattle raising and dry-farmed crop production The high cost of land leveling and relatively high cost of development of ground water supplies restricted irrigation development to low lying valley lands and terraces adjacent to streams., The introduction of sprinkler irrigation systems on a large scale is believed to be the major factor contributing to irrigation development in Upper Salinas River Basin.
-22- .
Dry- farmed grain and forage crops,, supplemented by increasingly larger acreages of irrigated alfalfa and pasture in the lands adjacent to the Salinas River
and its tributaries, are presently utilized in combination with the extensive dry grass mountain and foothill range lands for the production of beef cattle
In 1955 j the cattle and dairy industries accounted for 2>l\ per cent of the
total county agricultural valuation. In addition, large acreages of dry-farmed wheat are grown on the Carrizo Plain. The wheat produced in this latter area i3 a high gluten content Baart wheat which brings premium prices from the flour milling industry. Surplus grain and forage crops are exported for use by the dairies in the coastal area and in the Los Angeles area to the south.,
In the past, large acreages of dry-farmed almond orchards were cultivated in the vicinity of Paso Robles and Templeton. During the 1920*s through the middle lS^O's, as many as 16,000 acres of almonds were in produc- tion in this area. The cumulative effect of several damaging frosts and increased production costs along with relatively low prices paid for this product have resulted in reduction of acreage to about 7*500 acres.
As previously stated, irrigation was first practiced around Mission
San Miguel. Very little data are available on irrigated acreages for the years prior to 1920, the first year in which such data were included in
Federal census reports. A total of 5*320 acres was reported to be under irrigation in San Luis Obispo County in 1919* the majority of which was in the Arroyo Grande and Oso Flaco areas.
During state-wide investigations for State Water Resources Board
Bulletin No. 2, "Water Utilization in California", it was found that there were approximately 25*000 acres of irrigated land in San Luis Obispo County as of 1950, including truck crops, alfalfa, sugar beets, permanent pasture, and deciduous orchard. This figure was based on field surveys conducted by the
-23- «
U. S» Bureau of Reclamation and Division of Water Resources o A field survey- conducted during 1953 by the Division of Water Resources as a part of the
current investigation,, showed that irrigated lands totaled 3h»lk0 acres „ From the results of the surveys cited, it has been determined that alfalfa and irrigated pasture have become of increasing importance within the County., especially in Upper Salinas Valley- It was also determined that nearly all of the increase in irrigated acreage in San Luis Obispo County since the 1950 survey has occurred in the Upper Salinas Valley* Truck farming has continued to be the major agricultural endeavor in the coastal areas and accounts for about 22 per cent of the total county irrigated acreage
Urban development has*, to a great extent., paralleled growth of
agriculture as indicated by previously quoted population figures <, Industrial development has been limited generally to that required for the processing and
shipping of increasing amounts of agricultural products <> Notable exceptions include the recently completed steam-electric power generating plant of the
Pacific Gas and Electric Company at Morro Bay and the coking plant of the
Union Oil Company on Nipomo Mesa*
The annual harvest of almonds is processed at Paso Robles which also serves as a shipping point for cattle and grain° One of the largest almond packaging plants in the world is located in Paso Robles- Atascadero is a shipping point for poultry products. 0c«ano is a shipping point for the varied truck and field crops grown in the Arroyo Grande area. Home ports for the County's fishing fleet are located at Morro Bay and Avila. Several major oil company pipe lines cross the county., conveying crude oil from the Bakers- field, Taft, and San Ardo oil fields to offshore loading points at Avila and
Cayucos,.
U» S, Highways, Sign Routes 101 and U66, traverse the county as also
-21*- „
do several State highways . Over 1^200 miles of improved roads are included in
the county road system The coast route of the Southern Pacific Railroad
Company provides both freight and passenger service to Los Angeles and San
Francisco. Three public airports are located in the County and regularly
scheduled air service is provided the County by Southwest Airways
Two Army training centers, Camp San Luis Obispo and Camp Roberts,
occupy large areas within the County., Prior to I9I4I, Camp San Luis Obispo was
a National Guard Camp., In 19ljl, the camp was leased by the U. S. Army and
expanded as a wartime training facility.. During the period from June, 19^3 5 until December, 19kh> an average of about 15,000 troops were stationed at the
camp with a peak population in excess of 23^000 in March, 19UU- Except for a period of reactivation during the Korean hostilities as a Signal Corps training
center, Camp San Luis Obispo has been on an inactive status since 19U7 but has continued to serve as a National Guard and Reserve Officers Training Corps
training center., The hospital area of the camp is presently being utilized as quarters for the California Men's Colony, a unit of the State penal system*
A permanent facility for the Colony is planned for construction on a 200-acre portion of the Camp property., Camp Roberts was the largest infantry training center in the United States during World War II and although accurate figures are not presently available, it is known that at least 25>000 troops were stationed there during a portion of 19 li5« Except during the Korean hostili-
ties, Camp Roberts has also been on an inactive status, and is presently being utilized as an Army Reserve training center during the summer months
and occasionally by regular Army personnel for maneuvers «,
In addition to the facility at Camp San Luis Obispo, the State of
California operates three large institutions in San Luis Obispo County., These include a 3>Q00°acre campus of the California State Polytechnic College at San
Luis Obispo, the Atascadero State Hospital at Atascadero operated by the State
-25- Department of Mental Hygiene and the Paso Robles School for Boys near Paso
Robles operated by the California Youth Authority
Abundant recreational attractions are found throughout San Luis
Obispo Countye A significant portion of the County's income has, for some time, been derived from its tourist trade , and as the population of California increases , it is probable that the recreational facilities of San Luis Obispo
County will become one of the State's major attractions Camping and picnic facilities are located at 20 state and county parks located throughout the
County The most important Pismo clamming area in California is located
along the coastal strip from Shell Beach to the Santa Maria River « Ocean swimming is popular south of Morro Bay. Steelhead fishing is a major sport
along the entire County coast line» Atascadero Lake ? an inland attraction,
affords opportunity for swimming , boating , and fishing „ SLmilar facilities will be provided at Salinas Reservoir soon to be opened for public use, Los
Padres National Forest, occupying 37^4 square miles or about 11 per cent of the County area, provides abundant picnic and hunting facilities.
The total assessed valuation of San Luis Obispo County has been
doubled over the past decade « The assessed valuation of the County, as
reported by the County Auditor for the 1929-30 Fiscal Year, was $33 5 563*285<>
In 1939-1*0, the assessed valuation was $39 5 5l5 5 Ol5, and by 19l*9~50, it had climbed to $65,603, 955 • In the 195U-55 Fiscal year, the County's assessed valuation was reported to be $83*62?;, 365*
Hydro logic Units
In order to facilitate analysis of present and probable future water supply problems, San Luis Obispo County and certain tributary areas have been
divided into six hydrologic units , These units, the boundaries of which are
-26" shown on Plate 2 entitled "Hydrologic Units", have Deen designated Upper
Salinas, Coastal, Carrizo Plain, Guyana, Santa Maria, and San Joaquin*
Boundaries of the hydrologic units were defined after giving thorough consideration to those factors of water supply and utilization, topography, and geology, which affect hydrologic analyses. The boundaries of each unit are either coincident with the County boundary or else lie along well defined
topographic divides . To further facilitate analyses, one hydrologic unit was
divided into subunits. Subunit boundaries are also indicated on Plate 2 e
Areas of hydrologic units and subunits are presented in Table 3°
TABLIS 3
AREAS OF HYDROLOGIC UNITS AND SUBUNITS
« Area, in acres • Name s San Luis s Monterey « Kern « s Obispo County s County County s Total
Upper Salinas Unit 989,000 1*08,000 1,000 1,398,000
Coastal Unit Cambria Subunit 183,000 12,000 195,000 San Luis Obispo Subunit 177,000 177,000 Arroyo Grande Subunit 132,000 132,000
Subtotals 1*92,000 12,000 50li,000
Santa Maria Unit 55,000 55,ooo
Cuyama Unit 268,000 268,000
Carrizo Plain Unit 271,000 15,000 286,000
San Joaquin Unit 5U,ooo 51*,ooo
TOTALS 2,129*000 1*20,000 16,000 2,565,000
•27- CHAPTER Ho WATER SUPPLY
Water supplies of San Luis Obispo County are derived from precipita-
tion occurring almost entirely in the form of rainfall,, Ground water is
utilized intensively in certain portions of the County s and small amounts of water are utilized through surface storage or direct diversion of stream flow
Historically, there have been no imports or exports of water across the County
boundary© Within the County 5 however, inter-unit exchanges of water have been effected since 19U2, The water supply of the County is discussed and evaluated in this chapter under the general headings % "Precipitation'% "Runoff% 'Under- ground Hydrology", and "Quality of Water"o The following terms are used as defined in connection with the discussion of water supply in this reports
Annual—Pertaining to the 12-month period from January 1st of a given year through December 31st of the same year, sometimes termed the
calendar year
Seasonal —Pertaining to any 12-month period other than the calendar year*
Precipitation Season—The 12~month period from July 1st of a given year through June 30th of the following year.
Runoff Season—The 12-month period from October 1st of a given year through September 30th of the following year
Investigational Seasons —The three runoff seasons of 19£2-53<>
1953~5>U^ and 195>U~3>5>> during which field and office work on the San Luis
Obispo County Investigation was performed,,
Mean Period—A period of time chosen to represent conditions of water supply and climate over a long series of years
-28- •
Base Period—A period of time shorter than the mean period chosen
for detailed hydrologic analysis because prevailing conditions of water supply
and climate were approximately equivalent to mean period conditions , and
because adequate data for such hydrologic analysis were available,,
Mean—An arithmetical average relating to mean periods «,
Average—-An arithmetical average relating to periods other than
mean periods
In connection with the State-Wide Water Resources Investigation,
recently completed, it was determined that the $0 years from 1897-98 to 19li6-i47,
inclusive, constituted the most satisfactory period for estimating mean
seasonal precipitation generally throughout California,. Similarly, the 53-year
period from l89li-95 to 19l^6»lj7> inclusive, was selected for determining mean
seasonal runoff <> In studies for the San Luis Obispo County Investigation,
these periods were considered representative of mean conditions of water supply
and climateo
Studies were made to select a base period for hydrologic analysis of
the several units of the County, during which conditions of water supply and
climate would approximate mean conditions, and for which adequate data on water
supply, water utilization, and fluctuations of underground storage would be
available. For the purpose of surface reservoir operation studies, it was
determined that the 16-year period from 1935-36 to 1950-51 t inclusive, was the
most satisfactory in this respect . Average conditions of water supply during
this base period so closely approximated conditions prevailing during the mean period that they were considered to be equivalent. Average temperatures
prevailing during the chosen base period also closely approximated mean
temperatures.
-29- « »
The latter seven years of the chosen base period., 19bh-k5 through
1950=51* have been selected as representative of drought conditions through- out the County and consequently have been taken as the critical period for safe yield determinations of surface and underground storage reservoirs
There is evidence that other drought periods., such as the period from 1922-23 through 1935=36, were possibly of slightly greater severity., with regard to accumulated deficiency in water supply for certain reservoir sizes studied, than the period, 19U*-ii5 through 1950-51° Where adequate hydrologic data were available, the earlier drought period was studied.. In all cases, it was found that the difference in safe yield determinations resulting from use of the
later drought period was well within the limits of accuracy of the studies <,
Precipitation
San Luis Obispo County receives nearly all of its precipitation from
Pacific storms occurring generally during the months from December through
Marcho Precipitation, the source of all water supplies in the County, is consumed or disposed of in several wayss evaporation and transpiration from plant and ground surfaces soon after occurrence of rain| accumulation in pore spaces of the soil mantle, which source subsequently furnishes water to meet
consumptive requirements of vegetal cover | deep percolation to storage in pore
spaces of the underground water-bearing materials in absorptive areas $ and surface runoff
Precipitation Stations and Records
As of July 1, 19514* there were 69 active precipitation stations in
San Luis Obispo County, of which four were equipped with continuous recorders
Records from these stations, together with those from 81 other active and inactive stations in and adjacent to San Luis Obispo County provided sufficient data to ascertain the pattern of precipitation occurrence over the investiga- tional area. The longest continuous record in the County is that for the station at San Luis Obispo which began in l869o Records of precipitation are currently being maintained at 6k other stations in San Luis Obispo County having unbroken records extending over at least ten years. Locations of precipitation stations are shown on Plate 3, entitled "Lines of Equal Mean
Seasonal Precipitation". Reference numbers correspond to those appearing in
State Water Resources Board Bulletin No. 1, "Water Resources of California".
Numbers, prefixed by an appropriate county designation; i.e.., S» L. 0. 3 San
Luis Obispo County, or M., Monterey County, etc, have been assigned to those stations not included in Bulletin No. 1. Listed in Table k are selected precipitation stations and map reference numbers, together with station elevations, periods of record, maximum, minimum, and mean seasonal precipita«= tion, and sources of record. In those instances where it was necessary, precipitation records were extended to cover the 50-year mean period by correlation of available data with corresponding data from nearby stations having records covering this period. Descriptive data pertaining to all precipitation stations in San Luis Obispo County and vicinity, together with monthly records of precipitation not previously published, are included in
Appendix C.
-31- 289 2
TABLE 4
MAXIMUM, MINIMUM AND MEAN SEASONAL PRECIPITATION AT SELECTED STATIONS IN SAN LUIS OBISPO COUNTY
• Estimated: Maximum and
1 1 Period of : mean minimum
Map s s Elevation? reeord "seanonal seasonal Source precipitation reference; Station : (feet) s sprseipi- of
number i 1 U.S.G.S.s s 2 'feats, en Inches record
: datum i From 2 To 5 (inches ' Ssason of
2 of: depth) jLtiiSjL
SLO-1 Arroyo Grande No. 1 155 1904-35 15.4 194o-4l 34o74 U.S.3.R. 1908-09 1933-34 80 59 1910-11 1911-12 1913-14 1916-17 1918-19 1920-21 1922-23 1924-25 1936-37 1939=40 1953-54
G NOo 1 835 1915-16 1926-29 22 o3 194o-4i 35.91 u,.S.W.B. 1931~32 1944-45 1952-53 11.24 1946-47 1953-5H
3-050 Avila 115 1930-31 1939-40 17.2 1951-52 25.06 0,.S.B.R. 1941-42 1953-54 1933-34 9=20 & UO Co.
SL.0-7 Cambria Highway 60 1937-38 l?53~5^ 20«7 1940-41 380 38 SDH Maintenance Station 1938-39 9-53
SLO-J Cai-visso Plain No. 1 2,000 1930-39 1953-54 8.9 l«4o-4l 17»88 SLO FA 1950-51 5.02 (Cavanaugh)
3-5** ChoiaDG Hatch Ranch 1,975 1925-26 1953-5^ n.o 194o-4i 20.73 U.S.W.B. 1933-34 5° 57
3-59 Creston Pump Station 1,099 1924-25 1953-54 23.0 l>4o-4l 20,08 UO 'Co. 1338-39 6.04
3-58 Ernst Ranch 900 1930-31 1938-39 12c 7 194o-4l 25,094 Private l94o-4l 191*1-42 1932-33 6.15 1943-44 1953-54
3-358 Ester© 20 1929-30 1953-5*; 16 . 1940-41 31.86 SO Co. 1938-39 9»56
SLO-15 G-erst Ranch 1,500 1925-26 1953-54 24.3 1940-41 48.31 Private 1938-39 12»o6
SLO-18 Hearst Ranch 150 1937-38 1953-5^ 25 . 1940-41 46.79 Private 1938-39 12.58
3»o63 Huasna 770 1929-30 1931-32 19° 1940-41 37°63 U.S.W.B. 1933-34 1953-51* 1930-31 11.18 & SLO FA (G. Bair)
3-U9 Linn Ranch 800 1925-26 1953-5^ 16*5 1940-41 33.90 Private 1938-39 7-75
3-68 Niporao 360 1920-21 1953-54 15=2 1940-41 31.09 Private 1923-24 6.53 (A. Mehlschan)
32» 9 s -
MAXIMUM, MINIMUM AND MEAN SEASONAL PRECIPITATION AT SELECTED STATIONS IN SAN LUIS OBISPO COUNTY (continued)
; : Estimated Maximum and
: Period of ! mean ; minimum :
: Map Elevation: record : seasonal : seasonal Source
precipitation : reference Station : (feet) : :preoipi- : 0f b : ; number U.S.G.S.: % tation ; Inches record
: ( Season % of : datum : From ; To Inches ;
• : : : of depth) ; : depth
3-57 Paso Robles No. 1 74o 1886-87 1953-54 15-8 1937-38 3O069 U.S.W.B. 1897-98 4.77 a 3-067 Paso Robles 4NW 830 1938-39 1953°54 — — UoS.W.B.
3-069 Point Piedras Blancas 30 1905=06 1908-09 1946-47 12.49 U.S.WcB, 1939-40 1953-54 18.3 194o-4l 40.21
SLO-29 Quenzer (Radloff) Ranch 810 1930=31 1935-36 12.1 194o~4l 24.53 U.S.B.Ro 1937-38 1946-47 1950-51 5.54 & SL0 FA 1950-51 1953-54
SLO-30 Runitz Ranch (El Pomar) 1,150 1914-15 1953-54 16.4 194o-4l 28.24 SL0 FA 1923-24 4o50
3-64 San Luis Obispo 300 1869-70 1953=54 21.7 194o-4i 42.92 U.S.W.B. (Cal Poly) 1897-98 7.20
3-085 San Luis Obispo Tank Farm 118 1930-31 1953-54 18.7 194o-4l 37»77 U0 Co. 1938-39 9.91
SLO-53 San Miguel 625 1936-37 1953-54 1940-41 25.17 Private 1938-39 6.45 (G. Parker)
3-63 Santa Margarita 995 1919-20 1930-31 250 194o-4l 42.12 Private 1936-37 1953-54 1933-34 7.97 (S.P.Depot)
3-076 Santa Margarita 974 1931-32 1953=54 24.6 1940-41 43.30 Private (Tank Farm) 1938-39 IO.38 (U0 Co.)
SLO-35 Seven-X Ranch 1,200 1930-31 1942-43 4i.8 194o-4l 79.63 Private 1938-39 20.10 (Dee 1951-52 1953-54 Fitzhugh)
SLO-36 Shandon Highway 1*090 1937-38 1953-54 11.6 194o-4i 22 e 89 U0S.B0R* Maintenance Station 1947-48 6.23 & SDH
3-078 Shandon Pump Station 1,056 1935-36 1953-54 9°6 l94o-4i 18.99 U.SoBoR, 1950-51 5.14 & Private (SO Co.)
SLO-37 Simmler Highway 2,047 1937-38 1953-54 8*1 l94o=4i 18.08 SDH Maintenance Station 1950-51 4.4o
•33= MAXIMUM, MINIMUM AND MEAN SEASONAL PRECIPITATION AT SELECTED STATIONS IN SAN LUIS OBISPO COUNTY (continued)
Estimated Maximum and
9 Period of : mean minimum M .p ! :Elfeva%lor is ifeflftrd : seasonal seasonal Source r jfertoflo: station : 'fesrt) DroeipJ- proolritatior. °f t number % U.SoG.3. tati«m t Inches r*cor*r
' : datum : From "t To ! (Inches Season s of
• * • 1 of depth) : depth
3^7 Sodr. Lake 1,975 152V-26 19*^-47 8.7 1940-41 18.50 U.S.B.R. 1946-49 19-3-54 I933-34 5° 39 & SLO FA (D. Werling)
SLO-'S? Sue? Ranch 500 1909-10 1953-54 14.8 1940-41 30.02 Private 1912-13 6.29
3<=56 Tempieton 800 1925-26 1928-29 21.3 1940-41 38.79 SLO FA 1930-11 1953-^ 1938-39 10.79 (C. G. Corralt)
Broken records. I^br eviction Mane
U.S.W.B. United States Weather Bureau SLO PA San Luis Obispo County Farm Advisor U«S.CE» United States Corps of Engineers U.S.B.R. United States Bureau of Reclamation SDH State Division 0? Highways, San Luis Obispo Office SDP State Division of Forestry SLO RD No. 4 San Luis Obispo County Road District No. 4 PG&E Pacific Gas and El uo trie Company UO Co. Union Oil Company ? Co. Standard Oil *7©rrnany AMW Co, Atascadero Mutual Water Company
~3k« Precipitation Characteristics
As stated previously, precipitation occurs principally in the form
of rainfall, although infrequent light snowfalls are recorded in the interior portions of the County at higher altitudes. As shown by lines of equal mean seasonal precipitation depicted on Plate 3j precipitation over San Luis Obispo
County occurs in an irregular pattern ranging from a mean seasonal depth of about k2 inches at the higher elevations in the Santa Lucia Range to about eight inches on the Carrizo Plain. Precipitation generally decreases easterly and westerly from the Santa Lucia Range, increasing again slightly over the La
Panza Range . Higher elevations in the Caliente and Temblor Ranges have little apparent effect on the over-all pattern of precipitation in the eastern portion of the County where mean seasonal depth of precipitation is relatively low.
Amounts of precipitation occurring from season to season in San
Luis Obispo County are subject to wide variation, a characteristic which is typical of the South and Central Coastal Areas in particular and of the State of California in general. Seasonal precipitation at San Luis Obispo has ranged from 33 to 198 per cent of the 50-year seasonal mean. Maximum seasonal precipitation at this station occurred in the 19U0—Ul season when Ij2. 2 inches were recorded | whereas a minimum of only 7-20 inches fell in the season of l897-98e The minimum precipitation at this station during the base period was
10.39 inches, occurring during the 1938-39 season*
Long-term trends of precipitation at two typical stations are depicted on Plate U, "Representative Precipitation Characteristics in San Luis
Obispo County", on which relative magnitudes of seasonal precipitation at San
Luis Obispo and Paso Robles are graphically illustrated. Recorded and e-,
-35- estimated seasonal depths of precipitation and seasonal precipitation indexes for the period of record at four typical stations in various parts of the
County are presented in Table 5« The term, "precipitation index", refers to
the ratio of the amount of precipitation occurring at a given station during
a given season to the mean seasonal precipitation at that station, expressed
as a percentage*
36« - - „
TABLE 5
RECORDED AND ESTIMATED SEASONAL PRECIPITATION AT SELECTED STATIONS IN SAN LUIS OBISPO COUNTY AND VICINITY
sSan Luis Obispo % Santa Maria s Paso Robles : San Mi.guel • c sPrecipi- o :Precipi-s s Precipi- sPrecipi- ,
Season § tation s Inches ; tation ; Inches ce tation i Inches s tation % Inches
: index . depth : index s depth : index s depth s index s depth
1869-70 55 11.83 wm ^^ ... ._ •»«»£_, ui . (i rm/ am 71 60 12.97 __„ «„c •=*»„ ... . = «=> .c 72 12l* 27o02 ,=__ .... „=,_ ...... 73 S3 12.79 «*.. ._ ... .__ . ... 7U 9k 20.52 „„_ — — — ... -—
187U-75 91 19.69 ...... RHp —«...... 76 139 30.12 ... _„„ ___ .„- ...... 77 38 8.15 — -. ... __„ ...... 78 11*1 30.60 . _ ...... __„ ...... 79 5U 11.66 — — —- — ......
1879-80 119 25-82 MSB ... — CO ' ... >m> ... 81 109 23.69 — •»_ ...... _.« ... 82 79 17.03 ...... _,._ ...... 83 78 17.01 ...... _-„ ...... 82i 195 U2.i|0 — — ... — ... —
188U-85 81 17.59 M — a- ...... a „_„, ... -.<__ ...... 86 135 29 c 30 137 19.1*7 ... 87 76 16.514 66 9.36 — — = <=_ ... 88 85 18.35 83 11.77 90 lit. 30 ... — 89 90 19.51* 113 16. 0l| 100 15.814 __„ ...
1889-90 178 38.73 195 27.81 193 30.57 ... .!>. 91 90 19.51 85 12.10 101* 16.1*2 __ = —. 92 75 16.33 69 9.83 76 11.98 _<-«, ... 93' 11*0 30.1*0 121* 17.69 11*3 22.55 112 13.37 9k kS 9o8l 60 8.52 38 5.91* 35 14.20
189U-95 105 22.82 96 13.66 107 16.93 102 12.15 96 82 17.75 81 11.51 83 13. 11* 86 10.26 97 96 20, 75 106 15.11* 111* 17.96 101 12.02 98 33 7.20 i*o 5.70 30 1**77 26 3.15 99 80 17*33 88 12.52 73 11.53 66 7.90
1899-1900 79 17.21 65 9.23 71* 11.66 70 8.35 01 116 31.1*0 111* 16 c 28 11*1* 22.80 128 15.30 02 101 21.96 87 12.32 81 12.75 82 9.75 03 85 18.1*9 90 12.79 71 lie 21* 62 7.1*5 OU 78 16.99 79 11.18 92 ll*.5l 62 7.1*5
-37= RECORDED AND ESTIMATED SEASONAL PRECIPITATION AT SELECTED STATIONS IN SAN LUIS OBISPO COUNTY AND VICINITY (continued)
:SanJLui^ Obitspo Santa Maria Paso Robles ; San Miguel sPrecipi-s sPrecipi-s sPrecipi sPrecipi-s
Season s tation ; Inches s tation : Inches? sation Inches? tation 2 Inches
s index ; depth ; index s depth ; index depth s index ; depth
190U-05 109 23*56 11*5 20.65 126 19.89 122 11*. 59 06 130 28 .,11 125 17.86 96 15.23 106 12.61 07 115 21*. 89 127 18.02 139 22.00 13U 16,00 08 S3 18.06 98 13.96 97 15.31 107 12.81 09 11*5 31o38 160 22.81 153 21*. 21 150 17.92
1909-10 96 20,85 116 16.58 108 17.09 99 11 08O 11 159 3l*.l*2 11*5 20.69 168 26.61* 185 22 „11 12 79 17.11* 68 9.63 78 12.37 106 12.67 13 1*0 8.58 38 5.1*6 51 8.06 1*2 5.01 Ik 11*1* 31.21 132 18.86 139 22.02 161 19.20
I9il*-i5 130 28.17 133 18.93 158 21*. 96 178 21.21* 16 121* 26.93 117 16.66 136 21.51* 125 11*. 89 17 106 23.03 102 11*. 1*8 117 18.51 83 9.88 18 83 I80 06 111* 16.19 91 11*07 98 II.76 19 83 18 i 09 77 10.99 75 JLL 7 X. 90 10.78
1919-20 69 11*. 86 67 9.60 81 12.81 69 8.21* 21 89 19.27 78 11.01* 87 13.70 96 11.1*3 22 108 23.36 119 16.88 138 21.81 153 18.27 23 107 23 «28 87 12.1*3 93 15.1*5 97 11.51* 21* 38 8.19 1*1* 6.27 1*0 6.38 1*5 5.31*
192li~25 100 21.63 106 15.07 81 12.71* 65 7.76 26 87 18.82 71 10. 01* 93 11*. 79 88 10.50 27 111* 21*. 68 110 15.61 138 21.91 112 13.36 28 98 21.33 108 15.36 73 11.1*9 63 7.55 29 80 17.30 75 10.75 62 9.82 69 8.29
1929-30 69 ±1*.97 61* 9.18 69 IO.96 62 7.1*1* 31 67 11*. 63 61 8.72 76 12.10 81 9.69 32 137 29.75 118 16.78 105 16,59 113 13.55
; 3 73 15-7? 8C 11.1*1* 61 9.62 56 6.61* 36 69 0**97 Sh 1 .6? 73 11.62 10.27
193U-35 120 °5»99 131* 19.11* 131* 21.22 131 15.61 36 111 21*. 06 97 13.75 115 18.17 98 11.68 37 151* 33.29 11*7 20.98 11*5 22.87 138 16.51 11*3 30o98 152 21.53 19u 30o69 160 19.10 39 48 10.30 75 10.62 55 8.70 9x 5.66
.38- —
RECORDED AND ESTIMATED SEASONAL PRECIPITATION AT SELECTED STATIONS IN SAN LUIS OBISPO COUNTY AND VICINITY (continued)
:San Luis Obispo : Santa Maria : Paso Robles : San Mi guel
e> • , « ;Precipi- • sPrecipi- B :Precipi-m ;Precipi-
Season s tation s Inches ; tation : Inches s tation s Inches ; tation t Inches
1 index : depth : index % depth i index s depth : index ; depth
1939-1*0 115 2l*o 91 113 16. 09 98 15.57 106 12.66 ill 198 1*2.92 215 30.61* 193 30.1*8 218 26.08 1*2 109 23.61 120 17.01* 97 15.30 116 13.89 h3 120 26.06 121 17.26 109 17.21 111 13.23 hh 101* 22.1*7 102 H*. 56 78 12.30 107 12.81
19l*l*-l*5 98 21.28 79 11.29 76 12.00 78 9.31 1*6 83 17-99 78 11.11 71 11.20 77 9.25 1*7 67 ll*c27 66 9.36 65 10.27 68 8.16
1*8 72 15 = 51* 89 12.66 66 10.1*7 61* 7.60 1*9 68 ll*o67 61* 9.09 67 10.61 67 8.01*
19 1*9-50 87 18.96 69 9.81 71 11.29 71 8.1*8* 51 72 15 06I 65 9.21* 66 10.1*7 66 7.89* 52 135 29.30 126 17.97 111* 18.09 _. ... 53 78 16.95 76 10.86 69 10.99 _.« ... Sh 91 19.77 85 12.11 71 11.27 — ---
Average for 16-year base period, 1935- 36 throu gh 1950-51 103 22.30 103 11*. 69 98 15.1*8 100 11.95
Mean for • 50- year period, 1897-98 through 191*6-1*7 100 21.66 100 II4.2I4 100 15.82 100 11.93
Average for period of record 97 21.22 97 13.79 98 15.52 98 11.73
* Estimated.
-39- On the average^ approximately 90 per cent of the seasonal precipita= tion at San Luis Obispo occurs during the six-month period from November through April* Illustrative of monthly variation of precipitation in the
County is the mean monthly distribution of precipitation as recorded at San
Luis Obispo and Paso Robles 5 presented in Table 60
TABLE 6
MKAN MONTHLY DISTRIBUTION OF PRECIPITATION AT PASO ROBLES AND SAN LUIS OBISPO
Paso Robles San Luis Obispo Precipitation^ Precipitation
Month In inches s In per cent of Tn inches § In per cent of
of depth : seasonal total of d epth % seasonal total
July 0,01 Ocl 0.01 0.1 Augus t 0.02 0.1 0,01* 0.2 September 0.18 1.1 0.23 1.0 October 0.58 3.7 0c8l 3.7 November 1.20 7.6 1.67 7.7 December 2.60 16. U 3-,80 17-U January 3o60 22.8 >9k 23*0 February 3-h9 22,,1 lu62 20.8 March 2.77 17.>5 3-,60 16.6 April O.89 1-31* 6.2 May o.ljo 2,5 0.58 2,7
June 0.08 0.5 Pel It _0.6
TOTALS 15.82 100o0 21.68 100 oO
Runoff
The major sources of surface runoff within San Luis Obispo County are the highly predictive watersheds of the Santa Lucia Range. A large portion of this runoff in the streams draining the for going watersheds is presently wasting to the ocean. Runoff in the streams draining watersheds in
v, the e* stern 7 orticn of the Cownty is small because of limited p ecipi ta iiion.
ItO- Stream Gaging Stations and Records
There are few long-term records of runoff from streams within or
tributary to San Luis Obispo County. The longest active unbroken records of
stream flow in the County are for Santa Maria River near Santa Maria and Huasna
River near Santa Maria, both of which date back to December, 1929 o A continu- ous record of flow of the San Antonio River at Pleyto in Monterey County is also available for a portion of 1922, and continuously since 1929o Earlier records of stream flow are available for 10 stations which are presently inactive. With the exception of the record for Salinas River near Santa
Margarita, which is available for a portion of 1922, and continuously from
February, 1932, to September, 19U9, these earlier records were generally of short duration.
Records of stream flow in San Luis Obispo County are currently being maintained at lii gaging stations by the U. S. Geological Survey under provi- sions of federal-state and federal-county cooperative stream gaging programs^
These stations are located on Salinas River near Pozo, Salinas River above
Pilitas Creek near Santa Margarita, Salinas River at Paso Robles, Toro Creek
(Upper Salinas Unit) near Pozo, Jack Creek near Temple ton, Estrella Creek near San Miguel, Nacimiento River near Bryson, Nacimiento River near San
Miguel, Arroyo de la Cruz near San Simeon, Arroyo Grande Creek at Arroyo
Grande, Cuyama River near Santa Maria, Alamo River near Santa Maria, Huasna
River near Santa Maria, and Santa Maria River near Guadalupe. In addition, a record of quantity of water in storage in Salinas Reservoir on Salinas River is maintained by the U. S. Geological Survey, The Toro Creek station near
Pozo is maintained during the irrigation seasons only. The stations on
Estrella Creek and Nacimiento River near Bryson were established by the
-Ul- U. So Geological Survey in September , 195 k» and October , 1955 » respectively, in cooperation with San Luis Obispo County and are being maintained under the cooperative federal-state programs
For the purpose of supplementing available data, the Division of
Water Resources installed and maintained four stream flow gaging stations equipped with automatic water stage recorders on Huerhuero Creek near Geneseo
School , Estrella Greek near Estrella., Santa Rosa Creek at Cambria, and .Arroyo
Grande Creek below Santa Manuela School <> A station on Nacimiento River near
Bryson at the Monterey-San Luis Obispo County line,, equipped with a nonrecord«=
ing staff gage ^ read at least twice daily s was also maintained by the Division of Water Resources during the 1953=51i and 195^=55 seasons During the 1952=53 and 1953~5!t seasons , a gaging station was established and maintained by
Pacific Gas and Electric Company on Toro Creek (Coastal Unit) near State
Highway Sign Route No„ 1 in the vicinity of Cayucosc
Table 7 contains a list of the stream gaging stations discussed previously along with other stations considered pertinent to the hydrography of San Luis Obispo County, together with their map reference numbers shown on
Plate 5$ drainage areas , and periods, and sources of records. Map reference numbers on Plate 5 correspond to those used in State Water Resources Board
M Bulletin Noo 1 $ "Water Resources of Calif ornia Numbers, prefixed by an appropriate county designation^ ioe<>, So L» M San Luis Obispo County, or
Mo, Monterey County, etc° 3 have been assigned to these stations not listed in
Bulletin N « 1. Konbhly re^ocdo of stream dirj cl- ar^e n<>t previously published are included in Appendix D«,
°h2° • b£ . tO 1/) tO 10 tO 10 CO L0 13 CO W COd to CO CO CO CO CO CO CO CO to a> -a • » • • - - • > ve*t»r>oOf*opo>ao« « • S W • 0000 OOOCJ DOoOftOOlOlilbOOCO e> tjj OS <« (X o b cd St J" stst St St ir\ la unun m cd UN •Sn LSN •3n-3n * "UN ff, -3n 3n a\ as ctnon ON ON ON ON ON ON ON ON 1-1 H H i-H rH rH N ONO\ 5\ NJ-ri H •>|H CM o» \ •A »s „, •A o o o o ON ON vo o O O ON O ON O O o o O O O l-H rH fc, b_ rH on ONON rH ON r-4 ON ON ON ON ON ON ON cd a • • • a • * £> X> • o . ft e +i -p *» 0) +* +* -t? -e O O -p -P P P •P q, a. o. p. a cx-p -p &• P P- c £ft£ ft P\ P. a) cd cd o o cd o> O 4) a J3 ft- a> CSI CM <-l CM CM CNI CM CM C^ ON oncm oncm mc^H OJ ON CM ONCO o CM OI CM ON J" J" StSt ON UN ON UN ON UN O CM ON CM CM St Lr\ UN UN UN ON on on on on ON"on ON ON ON ON r-H ON ON ON ON ON ON ON ON ON ON ON ON r-H rH rH rH rH rH rH t-i r-t >» -P +» o ftofl b •P O fc ° ° > P > +» 3 a it 3 3O0NOc>a)ca>a) cd CD V a3 3 Ci^ C +» rH C T3 O <3 C ii t O c £rj cd C to -P tS 0) m -P CQ CQ ca 10 -p u CO «c\ UN MD r^-co ON rH CM li3« to w to to to • • • O C5 O O W J" =>- -=J- .3- ^* UMA UN UN UN ON ON ON OS ON r-i r-t «-> r-i ,-i O•» O«* * OOO<\ UN a 9 & a a. 0) u O 9> O to W to a to fi £ Jg s: si jz 60 s C I §> Sff O 5 b 00c £i5J2 £££ +» p *a +» -p -p ON C"\ CTN in D. CM fo • S on * ON ,-! .-< -a OOO C c ; C *» O a V a> w o a > O &. o -^ a o o «W Qj © O .-1 fa w m « CM f-v ON o on. fi. +> t3 rHCO H r-l NO S, ai C ON ^ Hi o05s «M >S O o J a* << O O CO t-^iJN.3- n • to «« S3 O C 0-! tO -W -H O -— OOO > • -) CO CO © OOO o o ^> Q CL. 1 UN UN lf\ r 2 CN ON ON si COOffi to o "3 NO CO ON UN\£. .3" +»H ct CM ON bo OOO to c OOO OOO o CM CM CM CM CM CM o r-t r-t i-l t-j r-i t-a t-t < E-> CO o n•z O o d od •ri >> rt rj trl i. *-t i. 00 1 1 1 a to B pj ri 3 •H ri >- . tTr-) •H -p S to qj 5 C a? P5 S to 3 to a no •H h to to O r-t Ml (i b CO Q. rj (j H3 -Wr . r In addition to periodic stream flow discharge measurements made for the purpose of rating gaging stations previously described, periodic and inter- mittent measurements of percolating and rising water were made at 6l stations on streams throughout San Luis Obispo County during the 1952-53 and 1953»51| investigational seasons,, Results of these stream flow measurements are included in Appendix Do Included in Appendix J are estimates of monthly run- off occurring during the base period , 1935-36 through 1950=- 51$ at selected dam sites discussed subsequently in Chapter IV Runoff Characteristics Runoff from streams in and tributary to San Luis Obispo County has historically varied within wide limits from month to month and from season to season. Though long-term records of runoff are lacking,, available records do indicate characteristic monthly and seasonal variations of runoff found throughout the Central Coastal Area of California, As evidenced by the pattern of precipitation occurrence , available runoff records indicate a relatively high intensity of runoff from streams draining the Santa Lucia Range with greater amounts of runoff occurring in the northwestern portion of the County where precipitation is generally higher,, Characteristically, seasonal and monthly variations of runoff follow very closely the seasonal and monthly variations of precipitation « Approximately 85 to 95 per cent of the flow of streams draining the watersheds of San Luis Obispo County occurs during the months of November through April on the average One of the most productive watersheds in San Luis Obispo County in terms of total volume of runoff is the Nacimiento River watershed. Unit runoff from this watershed for the 19li0~ljl season was 1*710 acre-feet per square mile and averaged about 600 acre-feet per square mile during the base period «, -16- Mean seasonal runoff is estimated to be 21^,600 acre-feet, and runoff during the base period averaged an estimated 210 9 270 acre-feet per season Approximately 53 per cent of the drainage area above the existing gaging station near San Miguel (Station 3~33) lies -within San Luis Obispo County, and approximately $0 per cent of the precipitation falling upon the watershed falls within San Luis Obispo County* However, based on measurements by the Division of Water Resources of the flow of Nacimiento River near Bryson (Station M-l), correlated with longer records of flow downstream, it is estimated that only about 1*8 per cent of the runoff of the Nacimiento River at the gaging station near San Miguel originates within San Luis Obispo County. Available records indicate that Arroyo de la Cruz is one of the most productive streams in San Luis Obispo County in terms of runoff per square mile of drainage area e By comparison with other streams in the area having longer records, it is estimated that unit runoff at the gaging station near San Simeon exceeded 3^000 acre-feet per square mile during the 19li0-l;l season, and averaged 1 9 080 acre-feet per square mile during the base period, that mean seasonal runoff amounted to l^ijQO acre-feet, and that runoff during the base period averaged Ui,750 acre-feet per seasonc As previously stated, unit runoff is generally greater in the northerly portions of the Santa Lucia Range than in the southerly portions where precipitation is less Runoff from Arroyo Grande Creek, though draining an area of about two and one-half times that of Arroyo de la Cruz, had an estimated average seasonal undepleted discharge during the base period of 20,730 acre-feet at the U. S. Geological Survey gaging station or slightly less than one-half the value estimated for the same period at the gaging station on Arroyo de la Cruzo Unit runoff during the l^liO-lil season at the -U6- Arroyo Grande Creek station was about ii20 acre-feet per square mileo Average unit runoff during the base period was about 200 acre-feet per square mile per seasono A comparison of seasonal variations in natural runoff of three typical streams in San Luis Obispo County is depicted on Plate 6, entitled "Runoff Characteristics of Streams in San Luis Obispo County" Long-term trends in natural runoff of two of the streams illustrating the apparent cyclic nature of runoff occurrence are also illustrated on Plate 6, Presented in Table 8 are estimates of the monthly variation in seasonal natural runoff of two selected streams > Nacimiento River and Arroyo Grande Creek TABLE 8 AVERAGE MONTHLY DISTRIBUTION OF SEASONAL NATURAL RUNOFF OF NACIMIENTO RIVER AND ARROYO GRANDE CREEK DURING BASE PERIOD, 1935-36 THROUGH 1950-51 s Nacimieni.o River Arroyo Grande Creek t near San Miguel i at Arroyo Grande % Month % Runoff ? in s Runoff , in % Runoff , ir i % per cent of % Runoff s in per cent of o : acre-feet seasonal total § acre-feet seasonal total October ™ 370 1.8 November ii 5 090 lo9 U30 2.1 December 18 , 020 806 830 UoG January 31,li*0 15.0 1,610 7»8 February 73,000 3iio8 5,860 28.3 March 59A70 28*1 5,900 28.5 April 20,370 9.7 2,8iiO 13.7 May 3,31*0 1«>6 l,lllO $0$ June 720 0o3 620 3.0 July 80 e=~~ U60 2*2 August 20 __. I43O Le 6 September 10 310 1.5 .. T _ TOTALS 210^270 100.0 20,700 100 cO U7- Quantity of Runoff As previously stated 3 few long-term records of rinoff in San Luis Obispo County streams are available » With the exception of the Cuyama and Huasna Rivera, no rvnoff records are available for streams within San Luis Obispo Count/ or tributary areao x^hich extend over the entire chosen base period o From studios of rainfall-runoff relationships and by correlation with ion^ex records from other nearby streams, using a modified form of a method originally described by H. C< Troxell in a report entitled "Hydrology of Weste: n Riverside County;, California", sufficient data were obtained to extend existing short-term runoff records o These studies provided bases for estimat- ing surface inflow to proposed surface reservoirs and surface inflow to and outflow from ground water basins selected for hydroiogic analysis. Estimated seasonal natural runoff and seasonal runoff indexes during the l6=year base period, 1935-36 through 1950«5l* at stations on four selected streams in San Luis Obispo County are presented in Table 9» 'US' h O O tACA-d- IAOn cacm ca tACAsO O rH sO H -d o rH G -CJ CNO-^H cAsO rint^- f— "IA CM C\J "IA _dtA On o > 0) a l-l C\J HCyHH H H 2 04 -H 34 CkO •H O P s G c G H -P CtJ o o o o o o o o o Q O O O O o o O O CO »> o o o o o o o o o o o o o o o o o o g o o o o OOcOcor^ CA O O sO CO CSJ vO «H X P O Q) CM SO O /H Os csj _3- o- os CA Os_d csj cm ^•O Os CM o "0 CSJ CO G O vOITvH sO H Os OssO 1A CSI r-i rH CSJ (A Os o HrlW fA rH rH ^» to > rH id -° PS _Q G •H 4» to o o o o O O O Q O O O O Q O o o o o CO •» CD o o o o O O O O o O O O O O o o o o a <+H Ch 1AO rH CV U\ C~- (A CO XA CM lAlACO Os "LA -sO rH TA CA rH rH CM CA CA Os o P O iH rH CSJ OS w CO 3 G O CM O SO _d CM l>- ,-1 CO SO CO lAsO OS CM C- CA sO o & o OS r-i - est ca r— O-IACM rH VA -du\ Os o O CD 3 c r-i CM rH CM r-i r-i rH 2 6 04 -H CO »H 3 H tO CO a G G T3 CO •H P CO O o O O O O O O O O O O o o o o o o o •» O O O O O O O O O O O O o O o o o o >s U O-d Osca O Os CSJ \asO SO. \A r-\ O -=t CO CO o- sO O CO *\ 9% vr, a\ •% 0^ *^ •% *fc 9% «\ «\ «\ «S •» •* <^ «\ @ U CA r-i OssO sO CO so -d-lA so 1A CSJ Os-d r-H-J- -d sO U G -3-V\0 sO CSJ XAsO CO a) a> O 1A C^-1A . U G o G >> •H P o O O O O O o o o o o o o o o u •» a) 8888 o o o o o o o o o o o o o o o u CO O O sO CM _d CASO -Cf os_ct-d- r>-so co co r>- OS f\ C% so r—co os O H CM CA-d TAsO C^-CO OS O rH u © u G CA » h >» G CO CA CA -d- 1 1 cO Os Os OS Os sO > CA CO rH rH H r-i CO 1A 6 -U9- Major Exchanges of Water Historically,, there has been no exchange of water across the San Luis Obispo (County line,, For the purpose of hydrologic analyses described in this and ensuing chapters, however, it was necessary to evaluate certain inter- unit and inter-oasin exchanges of water c Through the agency of the San Luis Obispo County Flood Control and Hater Conservation District, by the terms of a contract providing for operation of the reservoir by tne District with the Corps of Engineers, U. S. Army, water service from Salinas Reservoir has been provided to four consumers in the San Luis Obispo Subunit of the Coastal Unit since the Salinas Reservoir distribution system was placed in operation. They are, in order of magnitude of water consumed, City of San Luis Obispo, Southern Pacific Company, Costro Chrome Association, and Granite Construction Compapy<> Water service was provided the latter two organizations for only a brief period of time© Certain inter-basin exchanges of water are currently effected else- where in San Luis Obispo County. Theso include (1) pumped withdrawals from Arroyo Grande Ground Water Basin by the Water [Department of the City of Pismo Beach^ (2) pumped withdrawals from Old (Old Creek) Ground Water Basin by the San Luis Obispo County Waterworks District No, 8 (Cayucos) and the Paso Robles Beach Mutual Water Association foruse north and south, respectively, along the coast, and (3) pumped withdrawals from San Luis Obispo (San Luis Obispo Creek) Ground Water Basin by the Avila Water Company for use in the town of Avila. The diversions and use of the vaters of Old Creek by the Paso Robles Beach Water Association are covered by an application to appropriate unappro- priated water on file with the State Water Rights Board, for which a license, calling; for the diversion of 28,800 gallons p^r day, has been issued* •50- Metered and estimated records of diversions from Salinas Reservoir and exports from Arroyo Grande Basin by the County Flood Control and Water Conservation District and City of Pismo Beach, respectively, are presented for the respective periods of record in Table 10. Records of water production and use by other agencies effecting inter-basin exchanges of water were reported by those agencies to be unavailable© -51. TABLE 10 MAJOR EXCHANGES OF WATER BETWEEN HYDROLOGIC UNITS IN SAN LUIS OBISPO COUNTY In Acre-Feet 4 • Exported ; from 4 < : Upper Salinas Unit by s Exported from Arroyo Season s San Luis Obisp o Cou:nty s Grande Basin by Pismo ! Flood Control and Water s Beach Water Department • Conservation . District 1929=30 9Ga 31 100a a 32 100 a 33 100 3h 100a 193h-35 100a 36 HOa a 37 110 a 38 120 39 120a a 1939-iiQ 130 la 130a b a U2 50 I50 k3 960 190a hk 1,290 220a I9hh-16 i,5io 2UOa k6 1,680 260a hi 2,020 280a a UQ 2,320 280 a k9 2,230 2?O 19U9-50 2,260 290a 51 2,550 320 52 2, mo 330 53 2,1*70 360 $k 2,i;10 360 a. Estimated* b. Diversions commenced in July, 19U2* •52* Underground Hydrology Contained in this section is a summary discussion of the various factors affecting the occurrence, movement, and utilization of ground water in San Luis Obispo County. Data relating to the extent of present and probable ultimate ground water utilization, in addition to estimates of the safe seasonal ground water yield, are presented. Except for control provided through operation of Salinas Reservoir, regulation of the water supplies of San Luis Obispo County is accomplished mostly through utilization of storage in ground water reservoirs. Sufficient ground water supplies for all beneficial purposes under present conditions of development are found in valleys and many hill areas throughout the County, except in the Santa Maria Unit, and occur principally in alluvium and other unconsolidated sediments. Ground water reservoirs are replenished by percola- tion of surface waters in natural channels, by deep penetration of precipita- tion, by deep penetration of the unconsumed residuum of applied irrigation water, and by subsurface inflow. Disposal of ground water supplies is effected by pumped extractions, by effluent discharge, by consumptive use of water by phreatophytes, and by subsurface outflow. In connection with the discussion of underground hydrology in this bulletin, the following terms are used as defined: Key Well—A well chosen for study because it displays ground water characteristics that are considered representative of a given ground water basin or aquifer or a portion thereof. Free Ground Water—This generally refers to a body of ground water not overlain by impervious materials, and moving under control of the water table slope. Also termed unconfined ground water. In areas of free ground -S3- » water, the ground water basins provide storage to regulate available water supplieso Changes in ground water storage are indicated by changes in ground water level Confined Ground Water Body- -A body of ground water overlain by materials sufficiently impervious to sever free hydraulic connection with overlying water, and moving under pressure caused by the difference in head between intake and discharge areas of the confined water body,, Specific Yield—This term, when used in conjunction with ground water^, refers to the volume of water a saturated sample of the water-bearing material will yield by gravity divided by the volume of that sample, and is commonly expressed as a percentage,, Ground water storage capacity is esti- mated as the product of the specific yield and the volume of material in the depth intervals considered,, Specific Capacity—The number of gallons per minute per foot of drawdown produced by a pumping well. Drawdown—The lowering of the water level in a well in the local area around the well caused by pumping, measured in feeto Safe Yield—Refers to the maximum sustained rate of draft from a surface reservoir which could be maintained throughout a critically deficient water supply period. With reference to utilization of ground water supplies, the term refers to the maximum rate of net extraction from the ground water basin which, if continued over an indefinitely long period of years, would result in the maintenance of certain desirable fixed conditions o Safe ground water yield is normally determined by one or more of the following criteria: 1, Mean seasonal extraction of water from the ground water basin does not exceed mean seasonal replenishment to the basin -5U- 2 e Water levels are not so lowered as to cause harmful impairment of the quality of the ground water by intrusion of other water of undesirable quality, or by accumulation and concentration of degradants or pollutants 3* Water levels are not so lowered as to imperil the economy of ground water users by excessive costs of pumping from the ground water basin or by exclusion of the users from a supply therefrom., Overdraft- -Refers to the use of water in excess of safe yield where~ in any one or more of the criteria listed under "Safe Yield" are no longer satisfiedc The maximum safe yield of a ground water basin cannot usually be definitely evaluated until there is evidence of overdraft* As a result of this investigation, it has been determined that the only ground water basin wholly or partially within San Luis Obispo County in which there is evidence of overdraft is the Santa Maria Basin o The portion of the Santa Maria Basin within San Luis Obispo County is contained within the Santa Maria Unit© With increased use of water from presently underdeveloped basins, ground water levels will be further lowered during drought periods, thereby providing additional space in the basins for storage of percolating surface waters that would otherwise waste to the ocean during wet periods The net effect thereof would be an increase in yields of the basins » Since safe ground water yield is not a fixed value but may vary with pumping patterns, the magnitude of ground water basin utilization, the location of principal areas of recharge, and other inter- related factors, a further definition of the term is considered necessary* Therefore, as used in this bulletin with reference to those ground water basins considered to be suscep° tible of greater utilization, wherein no overdraft presently exists, the term "safe yield of presently developed ground water supplies" refers to the rate of net seasonal extractions therefrom with present patterns of land use under mean conditions of water supply and utilization.* Presented hereinafter are discussions of 19 ground water basins which have been identified in San Luis Obispo County as a result of this investigation o More detailed treatment has been given to two basins because of their relatively large storage capacity,, degree of present utilization* or greater abundance of hydrologic data Not included in the remainder of the group are numerous minor ground water basins scattered throughout the County which., because of their limited storage capacity and minor present water utilizations have not been given detailed consideration in this bulletin e Also not discussed in detail are ground water basins in the Santa Maria and Cuyama Valleys which have been extensively investigated by the U. S. Geological Survey,, results of which investigations are published in previously cited reports by that agencyc Shown on Plate 9 entitled ""Lines of Equal Elevation of Ground Water* Fall 195k" $ are the locations of the ground water basins* together with water wells employed in analyzing basin characteristics.. The wells are numbered by the system utilized by the U. S. Geological Survey* according to the township* range* and section subdivision of the Federal Land Surveyc In the portions of San Luis Obispo County not so subdivided* the township* range* and section lines have been projected*, Under the system* each section is divided into hO«=acre plots which are lettered as follows? =56= D C B A E F G H M L K J N P Q R Wells are numbered -within each of these i|0-acre plots according to the chrono- logical order in which they were located in the fieldo For example, a well having a number 26S/12E-I4NI would be found in Township 26 South, Range 12 East, and in Section k> It would be further identified as the first well located in the liO-acre plot designated by the letter "N". Most well numbers in San Luis Obispo County refer to the Mount Diablo Base Line and Meridian except in the southernmost portion of the County where the numbers refer to the San Bernardino Base Line and Meridian© Studies of underground hydrology included investigation of geologic characteristics of the basins, together with a preliminary quantitative analysis of replenishment and disposal of ground waters in certain basins, and qualitative analysis of ground water hydrology in most of the basinsc Geologic investigations included collection and analysis of prior geologic reports and maps, supplemented by discussion with geologists familiar with various portions of the County. Drillers logs for about 300 water wells and 93 oil wells were collected and analyzed. These data, together with additional information obtained by field surveys were utilized in preparing Plate 7 entitled "Areal Geology", and Plate 8 entitled "Geologic Cross Sections". The locations of the geologic cross sections are shown in plan on -57- Plate ?• Aquifers of significance to ground water utilization were identified from well data and are shown in the geologic cross sections delineated on Plate 8» Estimates of specific yield of water~bearing formations and ground water storage capacity were prepared primarily from a knowledge of charac- teristics of material classified in well logs. A detailed description of methods and procedures utilized in the preparation of these estimates is contained in Appendix B» Where there were sufficient data available on fluctuation of ground water levels, changes in storage occurring in ground water basins were estimated for the base period. Historical fluctuations of ground water levels in various basins are illustrated in Plate 10 entitled 8I "Fluctuation of Water Levels at Selected Wells , on which are presented hydro- graphs of ground water elevation at 12 wells in three of the 19 identified ground water basins. Water level measurements utilized in preparing plates relating to the occurrence and movement of ground water and fluctuations of ground water levels were obtained in the field by the Division of Water Resources or from Pacific Gas and Electric Company pumping tests* A summary of all known historical water level measurements at wells in San Luis Obispo County with the exception of those measurements reported by the U. S. Geological Survey for the Santa Maria and Cuyama Units is contained in Appendix Ee Based on the results of the foregoing studies and using stated assumption ; and criteria, the safe yield of presently developed ground water supplies in San Luis Obispo County exclusive of the Santa Maria and Cuyama Units is estimated to be about ljl,000 acre-feet per season. Under future conditions of development and water utilization, it is estimated that the maximum safe yield of the afore-mentioned area would be on the order of 70,000 -58- „ acre-feet per season. Results of studies and pertinent data for each of the ground water basins studied in San Luis Obispo County are discussed in the following paragraphs. Selected characteristics of ground water basins are listed in Table 11, Estimates of the presently developed and maximum safe ground water yield of each basin are presented in Table 12 -59- o o O O o o O O o O O O O O 1 o o 8 o o O o o o © O 8 o o J +* (O $* © o 8 "VO cm cn 8 CM CN UN o o UN O o o O 1 a) c-< w t, -p * <* a <=> » e» «, «> Cs 0% * <*, *4 •fc ». 1 B X> 9 o e o fH CM F-) VO CM n-J J=( H CM CM ON CM o O I •rt aj * a) a) o CM (-) J- 1 f n & «« o a 3 «i C W © »rt CO CO fs. UN UN UN rH s-« nH H i-l gH UN O UN O UN o i-t iH H ON w «5 o ) d" J* 1 CN CN UN O I O ON UN 1 l-J «M 1 «^ CM CN CM • O CM UN o O I o o © o o o O o o o o O « o o o o o o o o o o UN n-J cn CM CM CN tt UN o O CO I VO UN O CM o VO o o o o o o «^ o i MS CN o o ON o o o o o UN CM CN I s-» CN 3 «^ CN VO CM UN o LSN S£) o O CN CN o CM CN CO ON CN CN CM CO CN Zt ON $N UN 3 a. 3 o o o o o o o o o o o O o o o UN CO CO CO VO VO o O o J- f-t J* CM o o o o UN 1 CM t o o o O CM o o o CN «? CO CN CN VO J ON UN iri UN H o CM cH ft i-t i 1=1 a © » © « J* «fS i*-3 o-S UN UN VO CN CN VO o U ¥> -4 ON i-l © U a! ® sH S vt W) > + + + « o o o o O UN o o O O O o O o O a> © c ^i a VO CN CN CM CN CO CN CO O VO VO o o o C +» >H -P o H 1-1 5=8 o-J CM ON o © ? iH 8 g 1 t J3 *-« & o © © © o o © o o o o o i> o o c o O o o © o o ov o o o o o o o o © •fO 89 o o o UN CM VO CO CN U ON t^ UN CM CO J- CM o VO CM t-^ VO CN cv un r^ .=J- CM fv ON VO rH _? o o ** aJ S. at 8* % <* •> ts «. °* S« » g o H H 4>- ON UN CM VO CM CO r-3 * » o B- ia. i o 01 o & c 0) •H •O •rt -« o iH ai og o E- -60- TABLE 12 ESTIMATED PRESENTLY DEVELOPED AND MAXIMUM SAFE SEASONAL YIELD OF GROUND WATER SUPPLIES IN PORTIONS OF SAN LUIS OBISPO COUNTY AND VICINITY In Acre-Feet Unit, subunit, § Estimated safe seasonal yield and ground water basin : Presently developed! Maximum UPPER SALINAS UNIT Paso Robles 25,300 l*2,700a Pozo 300 1,000 Miscellaneous 1,300 1,300 Subtotals, UPPER SALINAS UNIT 26,900 1*5,000 COASTAL UNIT Cambria Subunit San Carpoforo b b Arroyo de la Cruz 200 U00 San Simeon 200 300b Santa Rosa 200 600b Villa 100 l,000b Cayucos 100 600 Old 300 300b Toro 100 500 Miscellaneous 200 200 Subtotals, Cambria Subunit 1,U00 3,900 San Luis Obispo Subunit Morro 600 1,500 Chorro 500 1,500 Los Osos 600 800 San Luis Obispo 1,900 2,000 Pismo 1,000 2,000 Miscellaneous 1,100 1,100 Subtotals, San Luis Obispo Subunit 5,700 8,900 Arroyo Grande Subunit Arroyo Grande 6,500 9,500 Nipomo 200 2,500 Subtotals , Arroyo Grande Subunit 6,700 12,000 Subtotals, COASTAL UNIT 13,800 2ii,800 CARRIZO PLAIN UNIT 600 600 SAN JOAQUIN UNIT TOTALS iil,300 70,U00 a<> Includes yield of Paso Robles Basin within Monterey County. b ffl Limited due to construction of proposed water supply developments -61= Ground watear beKdiras tdMLish to*. to« Unit inelbarie the Paso Be^etSi^asd Pease BSBssim.*- ISaese two basics comprise a total surface area of about -56% 9€QQ acres© Approximately 25 per cent of the Paso Robles Basin is located within Monterey County© Ground water basins of the Upper Salinas Unit are replenished primarily from uncontrolled runoff originating in the several major and minor streams tributary to the Salinas River above Wunpost railroad siding , and to a lesser extent from direct infiltration of precipitation* Water extracted from ground water storage in the Upper Salinas Unit meets over 95 per cent of the water requirement of an estimated present net irrigated area of 11,390 acres, as well as the entire water requirements of the communities of Paso Robles, Atascadero, San Miguel, Santa Margarita, and other smaller urbanized areas© In addition, minor quantities of ground water are extracted from rock fissures, less permeable sedimentary formations, and isolated pockets of alluvium located within the Unit© Paso Robles Basin© The Pasc Robles Basin generally coincides with the portion of the Paso Robles formation located within the Upper Salinas Unit as outlined on Plate 7A^ except that the drainage divide at the U. S, Geological Survey gaging station at Wunpost railroad siding is taken as the north boundary c The Paso Robles Basin covers an area of about 5 81 a 000 acres and contains some valley floor and terrace areas » Surface topography of the basin consists of hills with relief ranging up to 500 feet© Principal streams draining across the San Luis Obispo County portion of the basin are the Nacimiento River, Estrella Creek, Paso Robles Greek, and the main stem of the Salinas River which leaves the basin at Wunpost© «62<= Ground water storage in the Paso Robles Basin is replenished by- percolation of stream flow, precipitation, and return flow from irrigation and other useso Ground water is disposed of by pumped extractions to meet crop irrigation requirements and municipal and domestic demands, by consumptive use of phreatophytes in areas of high ground water, by effluent discharge, and by subsurface flow to Lower Salinas River Valley,, The Paso Robles formation of upper Pliocene and lower Pleistocene age furnishes water to most wells in the Paso Robles Basin, and consists of nonmarine sand, gravel, and clay up to 2,000 feet in thickness. The alluvium of Recent and upper Pleistocene age yields water to wells on the valley floor of the Salinas River and the Nacimiento River, but most of these wells also obtain water from the Paso Robles formation© The alluvium consists of stream deposited sand, gravel, and clay. Ground water is essentially unconfined in the Paso Robles Basin although confining clay beds of limited areal extent cause localized artesian pressures to exist with resulting upward movement of ground water Ground water moves from the periphery of the basin towards the Salinas River and Wunpost as shown by ground water contours on Plate 9&0 Details of ground water movement are complex because of the lenticularity of gravels and clays „ In topographically high areas, shallow wells generally have higher water levels than deeper wells while the reverse is generally true in topographically low areas. That water is moving upward under the influence of artesian pressures in low areas is also indicated by effluent flow or "rising water" in portions of San Juan, Cholame, Estrella, and Huerhuero Creeks . Irrigation wells generally yield about 500 gallons per minute, but a maximum of 3 5 300 gallons per minute has been reported. Specific capacity of wells averages about 15 gallons per minute per foot of drawdown with a maximum known value of 111. •63- Estimated average specific yield of the sediments of the Paso Robles Basin is about eight per cento Total estimated storage capacity below present static water levels is estimated to be several millions of acre-feet* The estimated practical extent of utilization of ground water storage is based primarily upon economic considerations » Irrigators in the west side of the San Joaquin Valley are known to be pumping ground water from depths of up to and exceeding U00 feet^ and irrigators in the Upper Salinas Unit are known to be pumping from depths in excess of 200 feeto Some preliminary analyses of the economics of irrigated agriculture in the Upper Salinas River area indicate that production of alfalfa can yield reasonable farm profits with water costs as high as $30 per acre If it is assumed that pumping costs , including interest and amortization on pump and well investment , as well as power and maintenance charges 9 average four cents per acre-foot per foot of lift 5 and assuming gross application of water of four acre-feet per acre, the resulting economic limit of pumping lift would be about 190 feet. This depth would be approximately 100 feet below present static levels <, For more remunerative types of agriculture ? as well as for municipal water supplies s this economic limit of pumping lift would be commensurately greater o The storage capacity in the Paso Robles Basin in the 100-foot zone below the present static levels of ground water in that basin may be as much as 3,000,000 acre-feet o The utility of this storage, however, is questionable at this time and cannot be completely evaluated due to the lack of sufficient basic hydrologic and geologic data Available historic data on ground water levels in the Paso Robles Basin indicate that, although static ground water levels therein have been subject to monthly and seasonal fluctuations, as well as localized cones of depression resulting from concentrated pumping drafts , there is no evidence of a perennial lowering of the water levels over the past 10 years " The general long-term stability of ground water levels in the Paso Robles Basin is illustrated by hydrographs of five selected wells presented on Plate 10, entitled "Fluctuation of Water Levels at Selected Wells The wells from which data were selected for presentation on Plate 10 were chosen because of their relatively longer records of measurements o Adequate records of well measure- ments in the Paso Robles Basin were not available to properly choose "key" wells in the sense as previously defined* As there has been no historical indication of overdraft conditions within the basin, the present safe yield of Paso Robles Basin is assumed to be equivalent to the present consumptive use of applied water or about 25,000 acre-feet per season a Because of the extremely large storage capacity s the maximum safe ground water yield of Paso Robles Basin may be expected to be a function of economic pumping lifts and mean seasonal recharge and not of storage capacity or configuration of the basin It is probable that the yield of the Paso Robles Basin could be increased very nearly to the limit of mean seasonal recharge if not prohibited by economic or water quality considerations, Because of the limited available hydrologic data, estimates of the maximum safe seasonal ground water yield of Paso Robles Basin are subject to consider- able error. Studies by the Division of Water Resources indicate that a substan- tial portion of the recharge to the Paso Robles Basin is derived from percolation of storm runoff in Salinas River and Estrella and Huerhuero Creeks <, Results of these studies indicated that the maximum safe ground water yield of Paso Robles Basin could be on the order of ij.3^000 acre-feet per season or about 70 per cent greater than the presently derived yield It is fully recognized that the foregoing figure may be substantially revised in the future as more adequate hydrologic data on which to base estimates are made available e -65- Pozo Basin and Other Miscellaneous Ground Water Sources „ The Pozo Basin is located upstream from Salinas Dam v and comprises a narrow strip of alluvium along the Salinas River and the valley floor of Pozo Creek with an area of about 3^600 acres The basin lies at an average elevation of about lj3>00 feeto The alluvium ranges up to 30 feet in depth o It is replenished by- percolation of stream flow,, precipitation^, and return irrigation flows,, It is depleted by pumped extractions s evapo-transpiration 5 and effluent flow Total ground water storage capacity in the Pozo Basin is estimated to be about 2^000 acre -fee to Available evidence indicates that the safe ground water yield of Pozo Basin is at least equal to the present consumptive use of applied water or 300 acre-feet per season on overlying lands s and that further utilization of ground water therein would probably increase the safe ground water yield up to a limit imposed by available storage 5 as described in Appendix B Accord- ingly,, the maximum safe ground water yield of Pozo Basin is estimated to be on the order of about 1^000 acre-feet or approximately one-half the total available storage capacity,, The safe yield of relatively nonwater-bearing formations tributary to Paso Robles and Pozo Basins is limited by the ability of the rocks to receive and transmit percolating water through their cracks and fissures „ Because of the variable nature of the occurrence of ground water in these formations and the limited geologic data available,, the maximum safe yield of these formations cannot be directly evaluated,, and can only be inferred from analysis of well measurements and historical production records „ For the purposes of this bulletin^, the safe ground water yield of sediments and nonwater-bearing forma- tions tributary to the Paso Robles and Pozo Basins has been taken as the present consumptive use of applied water,, or about 1^300 acre-feet per season,, =66* „ It appears that further development of this source to any appreciable magnitude is unlikely. Coastal Unit The Coastal Unit has been divided into the Cambria, San Luis Obispo, and Arroyo Grande Subunits» These subunits include several stream systems, each having a ground water basin underlying its lower reaches as shown on Plate 9B, entitled "Lines of Equal Elevation of Ground Mater, Fall, I9$h, Coastal and Santa Maria Units". Principal sources of water supply in the Coastal Unit include the 15 ground water basins shown on Plate 9B, import of surface supplies from the Upper Salinas Unit, and uncontrolled runoff originat- ing in streams draining the coastal slopes of the Santa Lucia Range» Negligible quantities of ground water are also obtained from rock fissures and isolated pockets of alluvium. Most of the ground water basins in the Coastal Unit have relatively small storage capacities and are filled nearly every winter by percolation of stream flow and precipitation . Several of the ground water basins in the southerly portion of the unit, however, have larger storage capacities and are not completely replenished by stream flow in all years of certain dry periods c The practical extent of utilization of ground water basins in the Coastal Unit is limited by physical rather than economic considerations Usable capacity in all cases is limited by either the total storage capacity or the minimum storage required to prevent sea-water intrusion° Hydrologic and geologic data are scant for most of the ground water basins in this unit 5 and as a result, quantitative hydrologic analyses of many of the basins was not possibleo =67- The total safe yield of presently developed water supply sources in the Coastal Unit is estimated to be about 19 ,,200 acre-feet per season, includ- ing 13^600 acre-feet from ground water sources as set forth in Table 12, and » . 5,600 acre-feet from Salinas Reservoir Most of the ground water basins in , the Coastal Unit are presently underdeveloped and it is estimated that the yields of those basins could be increased through greater utilization and consequent reduction of both effluent flow and excessive consumptive use of water by phreatophytes. However, as described in Chapter IV, it is anticipated that large surface storage developments will be constructed on several of the Coastal Unit streams. These developments would provide water service to down- stream lands and other lands in the vicinities of the developments, as well as furnish large quantities of water for export to concentrated areas of demand in the central and southern portions of the Unit- In several instances, ground water basins would be inundated by proposed reservoirs c In those cases the maximum safe ground water yield was taken to be no greater than the ultimate water requirements of overlying lands which would not be inundated Hydrologic characteristics of ground water basins in the Coastal Unit are discussed in the following paragraphs under their respective subunit headings © Cambria Subunit <, Ground water basins in the Cambria Subunit include San Carpoforo (or San Carpojo), Arroyo de la Cruz, San Simeon, Santa Rosa, Villa, Cayucos, Old, and Toro Basins, named for the principal streams which traverse thenio The eight basins range in size from San Carpoforo Basin, with 200 acres, to Santa Rosa Basin,comprising nearly 2,1*00 acreSo Elevations of the basins range from sea level to over 250 feeto .68- * Ground water storage in the Cambria Unit is replenished largely by percolation of stream flow and to a lesser extent from percolation of precipi- tation and return irrigation f low c Ground water supplies are disposed of primarily by effluent discharge, by pumped extractions, and by subsurface out° flow to the ocean* As previously stated, the town of Cayucos exports water from Old Basin by pumping from wells located near the mouth of Old Creek Records of historical ground water levels in this Subunit are unavailable except for those collected during the present investigationo .Residents con= tacted have indicated that water levels have been essentially the same for many years • This information along with available records of stream flow indicate that ground water basins have been fully replenished nearly every winter* Ground water occurs in alluvium of Recent and upper Pleistocene age underlying the lower reaches of the stream valleys» The alluvium consists of stream deposited sand, gravel, and clay up to 130 feet^in thickness, Records of historical water supply and utilization of the Coastal Unit are generally insufficient to permit more than an approximate determina- tion of the maximum safe ground water yield that could be developed. Available measurements of depth to ground water in wells indicate that all of the ground water basins have been recharged completely each winter in recent years by stream percolation, and that even if these basins were essentially completely dewatered during the preceding summer, natural stream flow would be adequate to recharge them in the following winter seasons* This would indicate that safe ground water yield of these basins is greater than the presently imposed net pumping draft. The total presently developed safe yield of ground water in the Cambria Subunit is assumed to be equal to the consumptive use of applied water, and is estimated to be on the order of 1,200 acre-feet per season* -69= o Under ultimate conditions of water utilization^ it is felt that the maximum safe ground water yield of these basins, which are all located adjacent to the coast line, would be governed by the total usable storage capacity, or storage capacity above sea level, as well as by percolation rates in the stream channels « In the cases of San Carpoforo, Arroyo de la Cruz, San Simeon, Santa Rosa, and Old Basins, the maximum safe ground water yield was limited to the net water requirements of lands which would not be inundated by proposed reservoirs discussed in Chapter IV e The maximum safe seasonal yield of the eight ground water basins in the Cambria Subunit was, therefore, estimated to be about 3 5 90Q acre~feet«, It is assumed that the yield of unregulated surface diversions and pumping from small pockets of alluvium will remain constant at about 200 acre°feet per seas one Separate estimates of the presently developed and maximum safe seasonal ground water yield of each basin comprising the Cambria Subunit, are presented in Table 12 San Luis Obispo Subunit. Ground water basins in the San Luis Obispo Subunit include Morrp^ Chorro, Los Osos, San Luis Obispo^ and Pismo Basins, named for the principal streams which traverse them. The four ground water basins have an aggregate surface area of about 25*800 acres, ranging from 1 5 270 acres for Morro Basin to the 9*680 acres comprising San Luis Obispo Basin. The basins range in elevation from sea level to about 350 feet. The San Luis Obispo and Pismo ground water basins may be conven- iently divided into upper and lower areas for descriptive purposes j the upper areas being located in the northwest-southeast trending San Luis Valley, and the lower areas in two north-south trending canyons traversing the San Luis Range „ •70. " Storage in the ground water basins of the San Luis Obispo SubunLt is replenished by percolation from streams, precipitation, and return flow of excess water applied for irrigation and other uses Ground water is depleted primarily by pumped extractions, by effluent discharge at times of high water level, and by subsurface flow to the ocean. A small residential area just east of Avila along the coast is supplied from wells located in San Luis Obispo Basin. This supply constitutes an export from San Luis Obispo Basin* Ground water occurs in alluvium of Recent and upper Pleistocene age, older sand dunes of upper Pleistocene age, and in the Paso Robles formation of lower Pleistocene and upper Pliocene age. Ground water in the basins of the sub unit is essentially unconfined, although clay lenses near the ocean may cause local pressure conditions . Ground water generally moves in the direction of surface slope, except in Los Osos Basin where it moves in a northerly direction in the older sand dunes as shown by ground water level contours on Plate 9Be Yields of irrigation wells in the alluvial fill generally average about 200 gallons per minute with a maximum known yield of over 700 gallons per minute. Specific capacity of wells averages about 15 gallons per minute per foot of drawdown with a maximum known value of $0 o Specific yield of the alluvium is estimated to average about 17 per cent. Records of measurement of ground water levels are virtually non- existent except for those collected during this investigation. Available evidence indicates that water levels fluctuate monthly and seasonally, but there is no indication of perennial lowering. This would indicate that these ground water basins have been replenished historically nearly every winter., A record of available measurements is shown on the hydrograph of well 29S/11E-19P1 on Plate 10, "Fluctuation of Water Levels at Selected Wells c -71- The presently developed safe yield of the ground water basins com- prising the San Luis Obispo Subunit is assumed to be equal to the consumptive use of applied water in those basins or about 5^700 aere»feet per season, of which approximately 1 5 100 acre-feet are obtained from minor unregulated surface diversions and miscellaneous small ground water bodies*, The maximum safe seasonal yield of ground water in the San Luis Obispo Subunit is not limited by the available storage capacity in all cases* The maximum safe seasonal yields of Morro and Ghorro Basins are limited by the usable storage capacity above sea level or about 2$ per cent of the total basin capacity as well as by percolation rates in the stream channels* In the case of Los Osos Basin* which has a relatively large ratio of basin storage capacity to average seasonal runoff , the maximum safe seasonal yield will be governed by the amount of percolation from stream flow and precipitation, and present safe yield is assumed to be equal to consumptive use of applied water on overlying lands « Present safe yields of San Luis Obispo and Pismo Basins are assumed equal to the consumptive use of applied water in these basins •> In the future, the safe yields could be increased by an amount no greater than the present effluent flow from these basins* The total maximum safe ground water yield of the San Luis Obispo Subunit is therefore estimated to be about 8 S °00 acre-feete It is assumed that miscellaneous unregulated surface diversions and uses of ground water from miscellaneous small ground water bodies will remain constant at about 1,100 acre-feet per season* Separate estimates of the presently developed and maximum safe seasonal ground water yield of each basin comprising the San Luis Obispo Subunit are presented in Table 12 o ~72« As stated previously , the City of San Luis Obispo presently derives a major portion of its water supply from Salinas Reservoir „ Approximately 2,600 acre-feet were imported from this source in 195>U° Because of diversion rights currently being exercised by the U„ S, Army and City of San Luis Obispo, the entire net safe seasonal yield of Salinas Reservoir, estimated at 5*600 acre -feet, is treated herein as a portion of presently developed safe yield of the San Luis Obispo Subunito A discussion of the operation of Salinas Dam and Reservoir, together with pertinent data on existing water rights is presented in Chapter III Arroyo Grande Subunit o Ground water basins in the Arroyo Grande Subunit include the Arroyo Grande Basin and Nipomo Mesa, The two basins have a total surface area of about 28,500 acres, of which 12, £00 acres comprise Arroyo Grande Basin and 16,000 acres comprise the Nipomo Mesa The basins range in elevation from sea level to about U60 feeto Ground water storage in Arroyo Grande Basin is replenished by percolation from streams, precipitation, return flow of applied irrigation water, and some subsurface inflow from Nipomo Mesa„ Storage in Nipomo Mesa is replenished primarily from percolation of precipitation. Ground water supplies are depleted in both the Arroyo Grande Basin and Nipomo Mesa by pumping, subsurface outflow, and evapo-transpiration Ground water has been exported from the Oceano area of Arroyo Grande Basin by the Pismo Beach Water Department continuously since 1929, estimated seasonal quantities of which are listed in Table 10 o Flow of surface water in Arroyo Grande Creek is closely related to subsurface flow in the alluvium. A substantial amount of surface water originating in Arroyo Grande Creek and Lopez Creek, an upstream tributary 5 °73- , percolates into alluvium in the upper portion of the Arroyo Grande Basin,, Effluent flow of Arroyo Grande Creek starts about three miles below the con- fluence of Lopez and Arroyo Grande Creeks, The amount of effluent flow continues to increase downstream^ reaching a maximum at the U, S Geological Survey gaging station at the town of Arroyo Grande , Below Arroyo Grande surface stream flow percolates to underlying ground water storage in the reach of stream down to the edge of the clay cap which is located a short distance below the bridge at Highway 1, Once surface water reaches the clay cap below Highway 1 ? very little percolation occurs and nearly all the water wastes to the ocean. Ground water occurs in alluvium of Recent and Upper Pleistocene age Pliocene age, Alluvium occurs only in Arroyo Grande Basin in this subunit and consists mostly of stream deposited sand, gravely and clay up to about 200 feet thick. Some alluvium near the coast,, however 9 has been deposited in a tidal lagoon or under similar shallow water conditions and consists of relatively impervious silt and clay. This silt and clay forms a confining clay cap in the coastal portion of the Arroyo Grande Basin, A few wells obtain water from the Older sand dunes in the area between Oceano and Arroyo Grande^, but most of the wells in this area obtain water from the underlying Paso Robles formation,, Wells in the Nipomo Mesa obtain water from Older sand dunes as well as from the underlying Paso Robles formation 8 In general^ yields of wells from the Older sand dunes are limited because of sanding of wells resulting from heavy drafts,* and for this reason most wells which penetrate to the Paso Robles formation yield more water than wells in the Older sand dunes. •7U- Irrigation wells in Arroyo Grande Basin yield up to 1,200 gallons per minute, but probably average about 360 gallons per minute, Specific capacity of wells averages about 1*0 gallons per minute per foot of drawdown with a maximum known value of 500. Based on an estimated average specific yield of 15 per cent, it is estimated a maximum of U0,000 acre-feet of ground water storage could be utilized without the occurrence of sea-water intrusion,. Irrigation wells in the Nipomo Mesa yield up to 1,500 gallons per minute, but probably average closer to 100 gallons per minute . Specific capacity of existing wells averages about five gallons per minute per foot of drawdown although a maximum value of 29 gallons per minute per foot of drawdown was noted. The average specific yield of water-bearing sediments was estimated to be about 18 per cent. No estimate was made of the usable ground water storage capacity of Nipomo Mesa because of insufficient geologic data e Ground water movement is indicated by contours on Plate 9B In general, ground water moves down Arroyo Grande Creek following the slope of the ground surface. It will be noted that a large cone of depression exists in the area north of Oceano, and available records indicate that this cone of depression has been present for most of the time since 19U5° Well measure- ments oceanward of this large depression, however, indicate that water levels are above sea level, and it is probable that sea-water intrusion has not occurred. It is probable that the pumping depression is caused by the relatively lower permeability of the Paso Robles formation which underlies the sand dunes and requires a steeper hydraulic gradient to transmit the water to wells in the area from the alluvium. It appears that, in the area to the west of oceanward side of the depression, the impervious clay stratum is sufficiently discontinuous to allow deep percolation of surface water from the old sand dunes into the Paso Robles formation, thus helping maintain •75- a seaward hydraulic gradient , Water level contours on Plate 9B also appear to indicate that ground water is moving from the Nipomo Mesa into Arroyo Grande Basin south of Oceano Historical measurements of water levels are more numerous for Arroyo Grande Basin than for any other part of San Luis Obispo County <> Long-term of six wells, hydrographs based on available records., are shown on Plate 10 5 "Fluctuation of Water Levels at Key Wells"*, These hydrographs and miscellaneous other wells measurements indicate a general decline in water levels during the period from 1933 to 1951|o However s water level measurements during the winter periods made during the current investigation and miscellaneous other measure- ments indicate that Arroyo Grande Basin is essentially filled during most wet seasons. It is 5 therefore 3 concluded that s although more extensive utilization of ground water in the basin has resulted in wider fluctuation of ground water levels £, the present ground water draft does not exceed the long term recharge of the basin. Available water level measurements in Nipomo Mesa indicate relatively little perennial change in water levels over the past ten years Representing the sum of consumptive use of applied water in the free ground water portion, total applied water in the confined ground water portion^ and present exports , the present safe seasonal yield of Arroyo Grande Basin is estimated to be about 6 ,,500 acre -feet. With maximum dewatering of ground water storage limited to li0 5 000 acre-feet in order to prevent sea-water intru- sion and dewatering of aquifers in the upper portion of the basin s it was determined that a net draft of an additional 3*»000 acre-feet of water could be imposed on Arroyo Grande Basin and still not violate any of the three safe yield criteria previously discussed. Conservation of this additional water would be effected through reduction of surface waste to the ocean and elimination of excessive consumptive use of water by phreatophytes. Surface •76= waste to the ocean would be reduced through greater utilization of the ground water reservoir by allowing more basin capacity to be made available to receive percolating waters The safe seasonal ground water yield of the Nipomo Mesa under present conditions of development and utilization is estimated to be 200 acre-feet per season* This basin is recharged solely through percolation of direct precipitation,, Through controlled pumping,, it is estimated that the safe yield could be increased to a maximum of about 2 ? £00 acre-feet per season This increase in yield would be effected largely through lowering of the water table and consequent reduction in consumptive use of water by the extensive groves of eucalyptus trees, as well as by reducing subsurface outflow,, Santa Maria Unit The major source of water supply for the Santa Maria Unit is the Santa Maria Ground Water Basin,, Small pockets of alluvium along Nipomo Creek also yield negligible amounts of ground water for use in the Nipomo area Principal sources of recharge to Santa Maria Basin include percolation from the Cuyama and Sisquoc Rivers and deep penetration of rainfall on lands over- lying the basin. As has been previously stated, no ground water studies were conducted in the Santa Maria Unit by the Division of Water Resources because of the detailed investigation currently being conducted in that area by the U. So Geological Survey in cooperation with the County of Santa Barbara,, Results of field and office studies conducted by the Geological Survey during the period from 19U1 to 19U5 are summarized in Water Supply Paper 1000 5 "Geology and Ground Water Resources of the Santa Maria Valley Area., California", It was estimated in Water Supply Paper 1000 that the safe seasonal yield of water-bearing deposits in the Santa Maria Valley area is in the order of -77= o 5>2 5 000 acre-feeto It was further estimated that with maximum utilization of the ground water supply in Cuyama Valley 5 a reduction in subsurface outflow from that valley in the amount of about 2 ,,000 acre-feet would be effected „ As outflow from Cuyama Valley constitutes a source of water supply for Santa Maria Basin,, the future safe seasonal yield of that basin would thereupon be reduced to about 5>0.»000 acre-feet,, The U S„ Geological Survey further estimated net pumpage from Santa Maria Basin to have been about 106^000 acre-feet in 195>0 5 with an average of about 6U 5 000 acre-feet per season during the period^ 1929 through 1950 With completion of Vaquero Dam and Reservoir on the Cuyama River <> an additional water supply will be made available for use in Santa Maria Valley. Under the proposed plan of operation., the portion of the reservoir storage capacity allocated to water conservation will be used for temporary detention of flood flows for later release to the Cuyama and Santa Maria Rivers at rates within the percolation capacity of the channel,, Recent studies by the Division of Water Resources in connection with the preparation of State Water Resources Board Bulletins Nos 2 and 3 show that the present net seasonal draft on Santa Maria Basin is about 91^000 acre- feet and that the safe seasonal yield is about 3>U<,000 acre-feet,, indicating an overdraft of about 37*000 acre-feet „ Operation of Santa Maria Basin in con- junction with surface storage in Vaquero Reservoir when completed will provide a new yield of about 18 5 5>00 acre-feet per season,, thus reducing the present average annual overdraft by about £0 per cent* The major source of water supply for the Cuyama Unit is ground water in the water-bearing sediments of Cuyama Valley herein designated as o Cuyama Basin „ The principal source of recharge to Cuyama Basin is the Cuyama River Cuyama Valley has also been investigated by the U„ So Geological Survey in connection with its continuing cooperative studies throughout Santa Barbara County „ Results of field and office studies in Cuyama Valley during the period 19hl to 19U5 are reported in Water Supply Paper 1110-Bc, "Ground Water in the Cuyama Valley, California",, The U S„ Geological Survey estimates the safe seasonal or perennial yield of ground water in Cuyama Valley to be on the order of 9*000 to 13,000 acre-feet, which quantities represent that agency's estimate of the "maximum amount of water that can be practicably salvaged from natural discharged The quality of ground water in Cuyama Valley is only fair, becoming even less desirable at depth The Geological Survey points out in its report the possibility of water quality considerations being the limiting factor in safe yield determination,, It is suggested that the rate of net ground water extraction may even be less than 9,000 acre-feet in order to avoid overpumping of the basin which could cause a mixing of the poorer with the better quality water,, As in the case of the Santa Maria Unit, the Cuyama Unit 5 as defined in this bulletin, does not encompass an entire ground water basin s and there- fore no determination of safe yield has been made for this unit<, Continuing studies by the U„ S„ Geological Survey in both Santa Maria and Cuyama Valleys should provide an adequate basis for more refined estimates of safe ground water yield for those areas, Carrizo Plain Unit Ground water in the Carrizo Plain Basin constitutes the only source of water supply to overlying lands at the present time c The Carrizo -79- „ Plain Basin, comprising some 172,000 surface acres,, is located in the largest area of internal drainage in the coast ranges Soda Lake is located at its center Carrizo Plain Basin is replenished to some extent around its edges by percolation of precipitation and stream flow resulting from infrequent cloudbursts „ Ground water storage in the basin is depleted by evaporation and pumped withdrawals o Small springs in the creeks draining into San Juan Creek on the northwest side of the Carrizo Plain suggest that a small amount of leakage occurs from the Carrizo Plain into the Upper Salinas Unit,, Ground water occurs in alluvium of Recent and Upper Pleistocene age and in the Paso Robles formation of Plio-Pleistocene age consisting of non- marine sand, gravel, and clay up to 1,000 feet in thickness. Only the north- west portion of the ground water basin is presently utilized for irrigation,, Here the quality of water in the alluvium is inferior to water in the Paso Robles formation, suggesting that the deeper 5 fresher water is not replenished by vertical percolation in the area of useo It appears that there is only a limited source of replenishment of the deeper water, and that increased use would probably exceed natural recharge,, In other parts of the Carrizo Plain, the water-bearing materials appear to be relatively impervious except near the edges of the basin on apexes of alluvial cones and contain water of poor quality Yields of the eight irrigation wells in the Carrizo Plain average about 500 gallons per minute with a maximum known yield at one well of 1,100 gallons per minute Estimated average specific capacity of irrigation wells is five gallons per minute per foot of drawdown with a maximum known value of 1$, No estimate was made of the total usable storage capacity of Carrizo Plain Basin because of insufficient geologic data 9 £Q~ „ Because of the limited recharge, the safe seasonal yield of Carrizo Plain Basin is believed to be small 8 Precipitation over the basin averages only about eight inches „ Although no runoff from storms was observed during the progress of the field investigation, it is known that percolation from runoff occurs during infrequent cloudbursts which occur in this area. Avail- able measurements of depth to ground water indicated no downward trend in water levels during the investigational seasons,, Historical water level measurements prior to the period of this investigation are nonexistento The safe yield of presently developed ground water supplies of the Carrizo Plain Basin has, therefore, been assumed to be equal to the present consumptive use of applied water or about 600 acre-feet Sufficient hydrologic and geologic data are not available on which to base an accurate estimate of the maximum potential safe yield of the Carrizo Plain Basin Available geologic evidence indicates the total ground water storage capacity of Carrizo Plain Basin could be on the order of several tens of thousands of acre-feet e The practicability of its full utilization is question- able at this time. With further utilization of ground water in the Carrizo Plain Basin and resultant lowering of ground water levels, a mixing of water and consequent degradation of the better quality water is possible Also, the threat of an unfavorable salt balance, which is likely to be build up through constant re-use of irrigation return flow if lands overlying the basin were extensively irrigated, would tend to limit the yield which could be obtained. For practical purposes, therefore, the maximum safe yield of Carrizo Plain has been assumed equal to the presently developed yield of 600 acre-feet per season^ Because of geologic conditions apparent at this time, it is believed that extensive irrigation of lands in the Carrizo Plain will cause the formation of a body of water at Soda Lake, replenished primarily from return -81- irrigation flows a With full development of the irrigable acreage discussed in Chapter III,, the lake would increase in size until a stabilized condition would be reached,, at which time the net evaporation from the lake surface would just equal the total return flow from applied irrigation water . Under the foregoing described conditions of development^ the lake surface would com- prise an estimated 7^800 acres* As a result of this investigation^ it was determined that water- bearing sediments s including Recent alluvium and a portion of the Paso Robles formation^ cover a portion of the San Joaquin Unit* There is virtually no ground water utilization in these areas at the present time a and since there are no records of depth to ground water at the few stock and domestic wells within the Unit, no estimate of safe seasonal ground water yield has been made, Precipitation over the unit averages less than nine inches and the safe ground water yield is probably insignificant* =82- • Quality of Water Surface and ground -water supplies in San Luis Obispo County are generally of fair to good mineral quality and suitable from that standpoint for irrigation and other beneficial uses However, there are certain areas in the Upper Salinas, Santa Maria, Cuyama, and Carrizo Plain Units where surface waters at low flow stages and some ground waters are considered to be less desirable because of abnormal concentrations of certain minerals,, Terms used in the ensuing discussion of quality of water are defined as follows? Mineral Analyses — The quantitative determination of inorganic impurities or dissolved mineral constituents in water c Quality of Water—-Those characteristics of water affecting its suitability for beneficial uses. Contamination '-— Impairment of the quality of water by sewage or industrial waste to a degree which creates a hazard to public health through poisoning or spread of disease Pollution—Impairment of the quality of water by sewage or industrial waste to a degree which does not create a hazard to public health, but which adversely and unreasonably affects such water for beneficial use c Degradation—Impairment of the quality of water due to causes other than disposal of sewage and industrial waste Hardness~A characteristic of water which causes increased consump- tion of soap, deposition of scale on boilers, injurious effects in some industrial processes, and sometimes objectionable taste, and which is due in large part to the presence of salts of calcium and magnesium. -83- Complete mineral analyses herein reported include determination of calcium, magnesium, sodium, potassium, bicarbonate, carbonate, chloride, sulfate, nitrate, fluoride, boron, total dissolved solids, electrical con- ductance (EC x 10° at 25° Co) and hydrogen ion concentration, pHo From the analyses, hardness, per cent sodium, and effective salinity are computed. Concentrations of principal constituents determined in a complete mineral analysis are reported in "parts per million" and "equivalents per million"' except for boron, fluoride, and total dissolved solids which are given only in "parts per million". Standards of Water Qualit Surface and underground waters of San Luis Obispo County are used for irrigation, domestic, municipal, and industrial purpose s« Surface waters are also used as stream and lake fisheries as well as for other recreational purpose So Suitability of waters for each of these uses depends in part upon the concentration and character of the dissolved mineral constituents in the waters. Irrigation Use Criteria commonly used to judge the suitability of water for irrigation use ares Chloride concentration, conductance (EC x 10^ at 25° Co), boron concentration, and per cent sodium,, (1) Chlorides are present in nearly all waters » They are not considered essential to plant growth, and may be especially harmful in high concentrations as they cause subnormal growing rates and burning of plant leave s, (2) Conducance (EC x 10° at 25° Co) carries the unit micro mho/ cm and is an indicator of total dissolved solids. For most waters, the total dissolved solids content in parts per million can be approximated by multiply- ing the conductance by 0c7° The presence of excessive amounts of dissolved salts in irrigation water will result in reduced crop yields e (3) Boron in small amounts (less than 0.1 ppm) is required for growth by most plants. Conversely plants usually will not tolerate more than 0<»5 to 2.0 ppm boron depending on the crop concerned. Citrus trees, particu~ larly lemons, are sensitive to boron in concentrations exceeding 0,5 ppnu (k) Per cent sodium as shown in water analyses is the proportion of the sodium cation to the sum of all the cations, and is computed by divid- ing sodium content measured in equivalents per million by the sura of the calcium, magnesium, and sodium contents also measured in equivalents per million, all multiplied by 100. Water containing a high per cent of sodium has an adverse effect on the physical structure of soil by dispersing the soil colloids and making the soil "tight", thus retarding movement of water through the soil. This in turn retards the percolation of the water and makes the soil difficult to work. The following excerpts from a paper by Dr. L. D. Doneen of the Division of Irrigation of the University of California at Davis, have been used in interpreting water analyses from the standpoint of their suitability for irrigations "Because of diverse climatological conditions, crops, and soils in California, it has not been possible to establish rigid limits for all conditions involved. Instead, irrigation waters are divided into three broad classes based upon work done at the University of California, and at the Rubidoux, and Regional Salinity Laboratories of the United States Department of Agriculture. "Class 1. Excellent to Good—Regarded as safe and suitable for most plants under any condition of soil and climate. "Class 2. Good to Injurious —Regarded as possibly harmful for certain crops under certain conditions of soil or climate, particularly in the higher ranges of this class. "Class 3« Injurious to Unsatisfactory— Regarded as probably harmful to most crops and unsatisfactory for all but the most tolerant. -85- "Tentative standards for irrigation waters have taken into account four factors or constituents, as listed belows Class 3 Class 1 Class 2 injurious to Factor excellent to good good to injurious unsatisfactory Conductance Less than 1,000 1,000-3,000 More than 3,00( (EC x 106 at 25° C) Chloride, epm Less than 5 5-io More than 10 Per cent sodium Less than 60 60=75 More than 75 Boron, ppra Less than 0o5 Oo5~2oQ More than 2.0 (End of quotation) The values shown in the foregoing tabulation are used only as a guide, since permissible linits vary widely with different crops, soils, and climatic conditions., Actual practice indicates that waters rated as Class 2 and 3 by the foregoing standards particularly in regard to conductance, are successfully used for irrigation in several areas in California* Accordingly, a new procedure for calculating salinity of irrigation water together with revised standards therefor has been suggested by Dr Doneen as follows i "This proposed standard for total salts of an irrigation water is based on the premise that the salts will accumulate in the soil due to evaporation from the soil surface and water used by the plants in transpirationo Plants usually remove only a small per- centage of the total salts occurring in the irrigation water,. As the soil solution becomes concentrated certain salts will precipi- tate» Because of the low solubility, the first to precipitate will be calcium carbonate, followed by magnesium carbonate and finally by calcium sulfate. These salts will not produce a saline soil© Other salts normally occurring in irrigation water in any signifi- cant concentration are extremely soluble and accumulate in the soil solution as salines© These salines are listed as 'effective salinity" e Therefore, calcium and magnesium carbonates and calcium sulfate should not be considered in establishing standards for total salinity as is now the practice in the use of electrical conductance, total parts per million or milli equivalents per liter concentration". >86* Using this method, Dr. Doneen has tentatively suggested the follow- ing criteria of effective salinity for classification of irrigation waters under three soil conditions t Class 1 Class 2 Class 3 excellent good to injurious to Soil conditions to good injurious unsatisfactory Effective salinity, in epm Little or no leaching of the Less than 3 3-5 More than 5 soil may be expected. Some leaching, but restricted. Less than 5 5-10 More than 10 Deep percolation or drainage slow. Open soils. Deep percolation Less than 7 7-15 More than 15 of water easily accomplished,. Review of various soil surveys in San Luis Obispo County made by the United States Department of Agriculture indicates that most of the irrigable and presently irrigated lands fall within the open soils classification and, for this reason, criteria for soils of this condition will apply throughout this discussion unless otherwise stated,, Domestic and Municipal Use . The "United States Public Health Service Drinking Water Standards, 1946" are probably the most widely used criteria for determining the suitability of water for domestic and municipal use. These standards are divided into two sections; one set of limits is mandatory and the other set is recommended. These standards are shown in the following tabulations -87- Limiting Concentrations of Mineral Constituents in Drinking Water U.S.P.H.S. Drinking Water Standards, 19 1*6 : Should not exceed Constituent ; ppm Mandatory Fluoride (F) 1.5 Lead (Fb) 0.1 Arsenic (As) 0.05 Selenium (Se) 0.05 Hexavalent chromium (Cr) 0.05 Recommended Copper (Cu) 3o0 Iron (Fe) and Manganese (Mn) together 0<>3 Magnesium (Mg) 125 Zinc (Zn) 15 Chloride (CI) 250 Sulfate (SO^) 250 Phenolic compounds (Phenol C^H^OH) 0.001 Total dissolved solids desirable 500 permitted 1,000 In consideration of the apparent direct relationship between the occurrence of infant methemoglobinemia (blue babies) and the presence of nitrates in drinking water it has been further recommended that limits be prescribed for nitrate concentrations. The California Department of Public Health has recommended a tentative maximum of 10 ppm nitrate nitrogen (hh ppm nitrates) for domestic waters© Total hardness is an important factor in determining the suitability of a water for domestic and municipal use. Compounds of calcium and magnesium are the principal causes of hardness although other substances such as iron, manganese, aluminum, barium, silica, strontium, and free hydrogen contribute to total hardness. The effect of hardness in water is primarily economic, in that its presence causes increased use of soap, which it coagulates to -88= „ form an insoluble precipitate. Hard water also will cause formation of scale in water and boiler pipes thus reducing the efficiency of boiler and plumbing systems. With proper treatment, hardness can readily be reduced to acceptable limits. Waters containing 100 ppm or less of hardness (as CaC^) are considered soft, those containing 101 to 200 ppm, moderately hard, and those containing in excess of 201 ppm as very hard. In this report, hardness is expressed as parts per million of calcium carbonate Industrial Use , The foregoing quality standards for domestic and municipal water supplies are considered applicable to most present and anticipated future industrial water uses in San Luis Obispo County, Industrial users usually accept water supplies which are suitable for domestic purposes and provide softening, demineralizing, or other treatment as required,, Data used to determine the quality of water in San Luis Obispo County included 114 complete and 14 partial analyses of surface water, and 160 com- plete and 36 partial analyses of ground water, A detailed discussion of water quality in various portions of the County, together with results of all avail- able analyses are presented in Appendix F, and are briefly summarized in the following sections under the general headings, "Quality of Surface Water" and "Quality of Ground Water", -89- Quality of Surface Water The mineral quality of surface runoff in streams of San Luis Obispo County varies greatly, both areally and with rate of stream flow,, The normal relationship of low mineral concentration at high rates of flow and higher mineral concentration at low rates of flow is indicated by many of the surface water analyses hereinafter presentedo As stated previously,, surface water supplies in most parts of San Luis Obispo County are generally of good mineral quality and are suitable for all beneficial purposes,, Available analyses indicate that most surface waters meet Class 1 or 2 standards for irrigation purposes . Except at low flow stages in some instances, surface waters in San Luis Obispo County also meet United States Public Health Service Drinking Water Standards,, Based almost exclusive- ly on analyses of low flow samples, waters of Cholarae Creek and Cuyaraa River appear to be of the poorest quality ^ being rather high in total dissolved solidso The boron content of Cholarae Creek water is also higher than the max- imum allowable for certain boron-sensitive crops „ Medium and low flow samples from streams draining both the east and west slopes of the Santa Lucia Range exhibit high, yet tolerable, degrees of hardness. It will be noted that much of the data on quality of surface waters presented and discussed herein and in Appendix F are based upon analyses of water samples taken from streams at times of relatively low flow, as the opportunity of obtaining samples at high flow stages from all streams did not generally occur during the investigational seasons o The water supplies developed by construction of surface storage projects described in Chapter IV will, to a large extent, be derived from stored flood flows which, by the nature of their occurrence, tend to be of better quality than some of the low flows sampled during this investigation. =90- It is therefore expected that water supplies derived from storage projects shown in Chapter IV will be generally of good to excellent quality. Results of analyses showing mineral quality of selected samples of surface waters in San Luis Obispo County are presented in Table 13. A compila- tion of the results of all known analyses of surface waters is presented in Appendix F. Locations of surface water sampling stations identified by map reference numbers listed in Table 13 and Appendix F are shown on Plate 5« -91- fa •p O. «> O S5 rH 1 cn a) TJ (0 O E co o CM CM P fa co eg O S OO OO ON O o (j (o i) a) a CM CM cn 6- X C O TJ (0 r-l 1 ® "O 0O o CO O o a 10 > -h E r-l OO o cn p -h in i-i a CM cn en r-i cn >n o >o o o o. E-" to a o l/V J- CO UN IfN ri O 1-1 o i-i O m 5. o e e • a. O o o o o E o cn o a. o O OC^N OCsj c se 1° o CMIO ir>|o i-l o —1 rH cH •H IIT\ c E r-l o |S cnl • o O 1 * »rl fa cm|o cm|o rH <1> iH o. •• »• •• CO L=t ON Id- +» 1° O E- Em c M P- CM I O cn|o r-l|0 r-l|0 rH|0 9 p CO O P •H re o •H E- •P IUN ION 1-H S in- ICM f° cn e- o n> a) Icm Ko z. x> PC w* << M onP. a, c 2 » 3 ! o|. a to o CO cn|o rH|0 Cn^rH o J J an <>! a) co o o ri E- •H << « a) o CO CO fa |o to- Ion 6- fc W fa <* X CO ps. k> 2 M • * o E o • OsJ • cnr% c o rn|o enjen cn|cM to j •H 4 O ss o 1° O |ir\ a) ON t-. Kn CO o Io ool-J j*- • *-J • w en sl'UNJC r-l|0 ir> CM vol^n LO ts o \0 r-l cn Pi • • CO t^ CO CO \DO o •H +» o (-. LT\ ON o CO M at o oo r-l cn cn r-l a- 55 o ir\ en af r-» VO VD W IN 1 a> TJ Cm 1 w> e -p un ri «1 fa O 0) it •h a) o a> CM O cn O C r-i O a JZ a c^, P-3 CM O (0 cn CO fa tj •a jd- cn J- (D| Q) UNO UN UN ir\ ir\ "^!£ if'irx • UN P E 1 O 1 r-l I J" 1 r-l a) -h cn cm cn o -f-» vd cn o-i CM CM ea|e- CM i-H CM r-l r-4 rH rH rH r-l rH CM r-l 1 1 1] 1 CM cn cn rH a> IS W) • BB TJ o fa TJ i -W 3 Nfc •H J3 o „ u at o i-i o co s c fa rt a> fa fa a> fa B k O q> aJ C a) «Q w ho-P •H O. fa £> , §?? 3 § TJ CO P d 9> H S3 fa a> a! 53 H CO CO g -h a 1 $**<<& S3 o c +» a O c a CO i o _ N E 0> a) •H fa a fa G fa 2 CO x Jri p •h e -h a> IO o m B c o > fa TJ a> a) -h fa a) a fa H fa CO <2 CO 05 «< -J co O O O 92- ' S-. 4» o) C-cd o CM O e< «> 25 CN cr\ ...... S .. .. rH I <*% J- cd 73 at OS UN CM f3 t m n o a fis CM o o) co cd cd a CN * 6- s: c o l-l T3 CO i-l I 0> T3 cd co > -H 6 00 & CM +s «H c-l r-\ c vo c*\ x) 0. •» e-i 10 w CM ITN O CM oa 8. « O. O O O J" 1 &. a 1 Q. O 1 OON a S5 H irj o-\|c J-|o r-l iH •H c e rH c O h d un| • *H b t^|o rH|C C\JpH rH r-1 5. •H E eg Jt -p O IONLPl fa c W • O a) O a 1-: m s 01 i o +» 1-1 C\ M 3 O 1 cr' n Sj' m en E- OO Ha n cm Ion p O CM un]i-( ol o e- 6- s ;*: co I o osjo 3 P X' «H J •f> [75 e- o a cd T) T3 J- c^\ CD 3^ UMfl trs o cr% +> s g i C^v I CM 1 CO o 4» ps o cu H E h & jCj XI O 10 0) cd o c C fc. CD cd $2 0> 0) O G u C CD cd •H Cu U X> b cd CD m cd +» H CO S t, a O ON LtS JrHCO cd 5* **-* 3 CD O M O Lf\ •P C O O rH •ij 6 1 3 I fa -rl o -o t. •P •H TO O O CO w | O ° •*-> +> rH -J fa -H J z J M << «< w ai 43 0. t/3 << a w II CP O CD cd XI O 73 tu Jrf .M +» r- cd B -93- Quality of Ground Water Evaluation of ground water quality in various sections of San Luis Obispo County shows mineral content to be variable, yet generally satisfactory for domestic, municipal, industrial, and irrigation uses. These ground waters are abnormally hard in some cases and require softening for municipal or domestic uses, as well as for certain industrial useso In some areas, notably Cholame Valley and Cuyama Valley, excessive concentrations of total dissolved solids, sulphates, or boron render the ground water injurious to unsatisfactory for irrigation use e It will be noted that, although some waters exhibit relatively high concentrations of dissolved solids as evidenced by electrical conductivity, these same waters have effective salinities well within reason- able limits for beneficial purposes. No general evidence of sea-water intrusion has been noted in ground water basins bordering on the Pacific Ocean. Results of analyses showing mineral quality of selected samples of ground waters in San Luis Obispo County are presented in Table LU. A compila- tion of all known ground water analyses is presented in Appendix F. Locations of wells from which samples listed in Table Ik and Appendix F were obtained are shown on Plate 9« -9U- r-> r*.:l Nfl J- ON CM CM CO ON 3n UN O » CM O H •H ft to a, o UN o UN E J- CM o CQ a a. o ft & a o IS [S I hS I I o o > * •|o onJo cm|o vo|o |UN ION IrH I ICO I O \\o J . cm| • JS-I • of* r-J » rnPi «—il •I* J^lrH UN|rH U^rH UMjrH oS|0 U^J 0* |CO Ion C^ VOlcO ONJ I CM I col o col C^MJ<"JO rH|ON. a sq' si" on. ion ION UN E- o olo onIun C N N M cc l Pi cm! • o f* J- . rH| « S ! NO i as on|lo •H tr-jON u-jco CM . 3 s oon 9 o a o IS te o 1 1 > ' c P |& 1 a, o 1 1 1 I 1 ONJO CM|0 i-h|o o^|o UN eg S 0N| » ON < o i CN ON|rH -d-|rH C<-\1 rH 3-|rH < 1 I d. * |S> J" P» ION» •^>|UN ON A a | ON co asA r-i CO VOO o o rH -PO UN ON UN X Rj ir\ t>. ON CO ON a CN •\ UN ON ON C^> ON W rH 1 X) £-. CO 0) CO b C rH ft 3 V UN N£> ON R^ CO UN B cd ^ rt E-" en ON O o O J" J" ON UN UN 3n UN 3n ^N +> ft UN t> r-\ O a b ON CM I J" u\ CO i ON •z. -3 N£> r-l a) I ON § CO rH CM f I CM c m M 4 pS ON. o-\ i rH • W to rH CM o & CM CN ON, -95- c a> CM 5 rt rO g Cm p iH •fi s< t, [0 s Bg E PU .p 1-1 1 c« a V ad LTv O •p X. to in CO a t » U E-i S C CTN i-l -P O i-t o o E- ei to C\! R •H a to c 5 CO E a, IDg VO o 6 tO Cxi <^ P* Q ft -p K«S c C S" o E- «O a o o 3 o1>H O o .^-^ 10 Cm « O W to fill § in S GO o o o CO cj O CM CJ U C rH ft 3 S ft t, S +» £ EO o en Is a E-i (0 T3 a ir\ th a> <-h -p ft .-1 d S CM CM ON o> o -96- Sources of Impairment^; f Water Quality Sources of impairment to the quality of waters in San Luis Obispo County include natural sources , domestic sewage, irrigation return water, industrial wastes, and sea-water intrusion* A brief discussion of the cause and character of each of these sources is presented in the following paragraphs Improperly constructed, defective., and abandoned wells are not actually sources of impairment to the ground water quality in themselves but may be important in the transmission of surface wastes, drainage waters, or leachate from cess- pools or septic tanks which could be sources of pollution, contamination, or degradation . Such wells may also provide avenues for interchange of waters between aquifers having different quality characteristics, and result in the deterioration of good quality waters,, To maintain the existing ground water quality in a basin, it is necessary to establish a balance between salt input to the waters of a basin and salt output and within any basin this salt balance generally controls the quality of water.. If salt input exceeds salt removal, an adverse salt balance exists and water quality will deteriorate due to the accumulation of salt. The sources of salt input to basin waters are many, including! dissolved minerals from soil and rock materials s agricultural fertilizers, industrial wastes, and domestic wastes. Normally, the only major sources of salt removal are surface and subsurface water outflows and water and waste exports Natural Sources o San Luis Obispo County has a few areas where poor quality of ground water exists due to natural degradation. In the Salinas Unit, poor quality ground water is found in several areas which are in the vicinity of notable structural features. These areas includes Cholame Valley along the San Andreas fault, San Juan Valley along the San Juan fault, -97- „ portions of the Salinas River Valley along the Paso Robles fault and between the Bradley anticline and the San Miguel syncline c The poor quality water found adjacent to the faults is probably due to the increased mineralization of ground water exposed to faulted and fractured rock and mineral material 9 and to contact with gases and mineralized juvenile waters moving up along fault fractures The source of poor quality water encountered in the area between the Bradley anticline and the San Miguel syncline is not known j however s several possible sources do existo The higher mineral content of this water may be due to connate waters retained in this area by the structural folds s to ground water replenishment from poor quality water moving in from Cholame and San Juan Valleys through Estrella Creek system,, or to unmapped faults which may traverse the area. The poor quality water in these areas can be a source of degradation to neighboring waters as they move under influence of water table conditions Ground water of Cuyama Valley was reported by the United States Geological Survey in Water Supply Paper 110=B S to vary considerably from one part of the valley to another It was further reported that the ground water was generally rather high in dissolved solids and a in most cases, ranged in hardness from 800 to 1^200 parts per million,, Because of the meager data available to the Geological Survey at the time of their study 5 no explanation could be given for the marked variation in quality which had been observed,. The waters of Cuyama and Santa Maria Valleys show excessive concen- trations of sulfate ion and total dissolved solids o The gypsum deposits in the upper reaches of the Cuyama River are largely responsible for this degrada- tion of surface and ground water « Excellent crop yields are obtained^ however s using this water 5 and only continued study will reveal the future results of this degradation. -98= „ Dome£jt±e ^jevf^o Domestic sewage returning to ground water through cesspools, septic tanks, and leach lines, or from community treatment plants, is of higher mineral content than source water. In a report entitled ^Waste 39 Water Reclamation and Utilisation , dated 195>h, the California State Water Pollution Control Board listed increases in the mineral content of domestic sewage of 20 to $0 ppm in chlorides, 30 to 60 ppm in sodium, and 20 to I4.O ppm in total nitrogen,, These increases in mineral content are so small, however, that domestic sewage may be considered a satisfactory source of ground water replenishment in San Luis Obispo County, and from this standpoint susceptible of treatment and conservation,. Several ground water basins in San Luis Obispo County, including Paso Robles, San Luis Obispo, and Arroyo Grande Basins, are partially recharged, either directly by sewage treatment plant effluent or by return flow from effluent applied as irrigation water However, as can be seen from the results of analyses published in this bulletin, many of the ground waters of San Luis Obispo County are rather ha.rd Concentrated salt wastes resulting from the regeneration of individually owned softening units could eventually render the quality of sewage unsuitable for re-use, and cause localized pollution problems o Similar problems could be created by discharges from central regeneration plants Irrigation Return Mater Irrigation of agricultural crops requires application of water in excess of the consumptive requirement for water in order to prevent undue build-up of salts in the root zones 6 This excess water may contain from two to as many as ten times the salt concentrations found in the original water supply In areas where irrigation return water can percolate to the ground water, it may constitute an important source of degradation to the water supply =99. Industrial Wastes o The development of natural resources and the growth of industry , including agriculture, in San Luis Obispo County will create waste disposal problems* Whenever harmful liquid or water soluble industrial wastes are discharged into stream channels s into the ground, or into unlined sumps , they constitute a threat of pollution to underlying ground water Sources of industrial wastes in San Luis Obispo County include the oil industry, an almond processing plant., slaughterhouses, chemical companies, and refuse disposal sites „ Wastes derived from the oil industry include connate brines of high salt content pumped from the oil sands, and contaminated "drilling muds",, Wastes from the almond packing plant usually contain high concentrations of sodium chloride <, Wastes from slaughterhouses are usually of organic nature which, if not suitably treated or handled may produce septicity in water supplies, with accompanying foul odors Chemical companies can produce wastes of varied types, and in most cases they would be harmful to ground waters if not disposed of properly. Refuse disposed in dumps will, on decomposition, release salts, which , when dissolved by rainfall or applied water, may percolate to ground water e Sea-Water Intrusion s The ground water basins in San Luis Obispo County, which border the Pacific Ocean 5 are geologically susceptible to sea- water intrusiono There are no known structural barriers to prevent the land- ward movement of sea water, and water-bearing materials which form these ground water basins appear to be directly connected with the ocean A landward gradient in the ground water surface is necessary for sea-water intrusion to occur Available well measurements indicate that a seaward gradient has been maintained historically in all coastal ground water =100- basins. Furthermore, except in one instance, available mineral analyses do not indicate that sea-water intrusion of coastal ground waters has taken place. Fligh chloride ion concentrations are reported in historic analyses of the water from a well serving Morro Bay State Park located near the shore of Morro Bay. Excessive withdrawals from that well have apparently lowered the pumping level in that well to a position below sea level*. Although sea-water intrusion has not generally occurred, this does not preclude the possibility of its occurrence in the future. Any increase in ground water utilization or change in pumping pattern in coastal basins which reverses the seaward water table gradient could result in sea-water intrusion, and this should be considered in any plans for future ground water development and utilization. A continuing monitoring pro grain including the measurement of coastal wells and the collection and analyses of water samples therefrom, will be necessary to ascertain the imminence of sea-water intrusion in the future. -101- o CHAPTER III. WATER UTILIZATION AND REQUIREMENTS Water is beneficially used in San Luis Obispo County at the present time for irrigated agriculture and for municipal and domestic purposes. Irrigated agriculture is the largest user of water, and it is considered that it will remain so in the futurec Water supplies are obtained largely by pumped withdrawals from ground water storage , and, to a lesser extent, by direct diversion from surface streams* Salinas Reservoir on the Salinas River is the only major surface storage development supplying water to lands in San Luis Obispo County The gross area within San Luis Obispo County has been shown to be about 2<,12° i,000 acres. It was found during this investigation that about 333$QOQ acres or 16 per cent of this gross area can probably be developed for irrigated agriculture or residential and urban usee The remainder of the area consists of relatively rugged mountain terrain not susceptible of agricultural development© It was also found that, while there has been a substantial increase in irrigated agriculture in San Luis Obispo County in recent years, this development has not been as rapid as the phenomenal increases experienced in certain other portions of the State o Intensively developed areas of irrigated agriculture are found in the Santa Maria Valley, lower Arroyo Grande Valley, and smaller localized areas along the upper Salinas River. About 38 per cent of the lands found to be potentially irrigable are located on the Carrizo Plain and in the Cuyama Valley lying at relatively high elevations, above which very little tributary runoff originates. Because of their remote location and high elevation, these lands are limited as to crop adaptability and will require expensive works to provide irrigation water service* Large portions of these lands, as well as the lands in the Upper 102- Salinas Unit 5 are presently dry-farmed and may oe expected to continue to be so used in the future until such time as the pressure for the products of higher types of agriculture makes it feasible to provide water service thereto.. Development of irrigated agriculture is expected to center generally in the Upper Salinas Valley* The rapidity of this development will depend to a great extent upon the capability of the underlying Paso Robles Basin to support increased ground water extractions. Full satisfaction of the water- using potential of this area will require construction of local surface water supply developments and facilities for importation of water from outside sources as described in Chapter IV. It is anticipated that increases in agricultural activity will result in a proportionate increase in population of urban communities through- out the County. Further., the lands along the coastal portion of the County are especially suited to urban and recreational development such as has occurred in other ccastal areas of California*, It is expected that increasing numbers of people will be attracted to this area because of its equable climate and scenic attractions* The nature and extent of water utilization and requirements for supplemental water in San Luis Obispo County., both at the present time and under probable conditions of ultimate urban and agricultural development, are considered in this chapter* In connection with the discussion, the following terms are used as defined? Wa t er_Ujbijd_a g'.t?-_on°' -Us ed in a broad sense to include any employments of water by nature or man,, either consumptive or nonconsumptive, as well as those irrecoverable losses of water incidental to such employment, and is synonymous with the term "water use",. =>103- Demands for tfater~- Those factors pertaining to specific rates, times, and places of delivery of water*, losses of water, quality of water, etc, imposed by the control, development, and use of water for beneficial purposes. Water Requirement—The amount of water needed to provide for all beneficial uses and for irrecoverable losses incidental to such uses Supplemental Water Requiremei?t°-"The water requirement over and above the sum of safe ground water yield and safe surface water yield under either present or ultimate conditions of development of water use* Consumptive Use of Water- --Water consumed by vegetative growth in transpiration and in building of plant tissue, and water evaporated from adjacent soil, from water surfaces, and from foliage,, It also refers to water similarly consumed and evaporated by urban and nonvegetative types of land use. Applied Water"" The water delivered to a farmer's headgate or from a well in the case of irrigation use, or to an individual's meter in the case of urban use, or its equivalent. It does not include direct precipitation*) Ultimate- «This refers to conditions estimated to be existent after an unspecified but long period of years in the future when development will be essentially stabilizedo It is realized that any present forecasts of the nature and extent of such ultimate development, and resultant water utilization, are inherently subject to possible large errors in detail and appreciable error in the aggregateo However 5 such forecasts, when based upon best available data and present judgment, are of value in establishing long-range objectives for development of water resources <, They are so used herein with full knowledge that their re-evaluation after the experience of a period of years may result in considerable revision* Water utilization and requirements are discussed and evaluated in n this chapter under the general headings; "Present Water Supply Development , -10U- "Land Use", "Unit Use of Water", "Present Water Utilization", "Probable Ultimate Water Utilization", "Demands for Water", and "Nonconsumptive Water Demands". Data relating to supplemental water requirements are discussed under the two general headings: "Present Supplemental Water Requirements" and "Ultimate Supplemental Water Requirements". Present Water Supply Development Present water supplies within San Luis Obispo County are largely obtained by pumping from ground water storage. As reported in the 1950 federal census, only 3*100 acres or about 11 per cent of the total irrigated area was supplied by surface diversions from streams and springs. Most of the diversion structures serving irrigated lands are temporary in nature and over half of the lands so served receive supplemental water from ground water sources. Salinas Reservoir, on the Salinas River, is presently a source of water supply for Camp San Luis Obispo and the City of San Luis Obispo, From a canvass of wells conducted during the investigation, it was determined that there are approximately 780 irrigation wells within the County. Approximately 80 per cent of these wells are equipped with pumps of heavy draft having motors of five horsepower or more. In addition, 55 wells, all equipped with pumps of heavy draft, supply water for urban and industrial use. In addition, a large number of wells of small draft supply limited amounts of water for domestic, garden, and stock uses. Major Water Supply Developments As stated previously, the only major surface water supply develop- ment presently serving lands within San Luis Obispo County is the Salinas Reservoir on the Salinas River with its conveyance system leading to the -105- vicinity of the City of San Luis Obispo* Although Nacimiento Reservoir is located within San Luis Obispo County, the Monterey County Flood Control and Water Conservation District does not presently contemplate serving water to lands within the former county from that source. Nacimiento Dam and Reservoir, located at a point identified in reports of the Division of Water Resources as the "Winchester Ranch Site" on the Nacimiento River, is designed to provide water conservation and flood control benefits to lower Salinas River Valley in Monterey County. The dam, now substantially completed, consists of an earthfill struc- ture with a height of 210 feet above stream bed, a crest length of about 1,500 feet, and a spillway crest elevation of 800 feet above sea level. The total reservoir storage capacity is about 350,000 acre-feet. It is understood from statements of officials of the Monterey County Flood Control and Water Conservation District that a portion of this storage capacity will be used for flood control purposes Nacimiento Dam and Reservoir, if operated entirely for water conservation purposes, would have an estimated net safe seasonal yield of about 73,000 acre-feet. Construction of Vaquero Dam, as a major feature of the authorized Santa Maria Project, was begun on July 1, 1956, and is scheduled for completion in 1958. Although the Santa Maria Unit will receive substantial flood control and water conservation benefits from this project, the major portion of benefits will accrue to the Santa Barbara County portion of the Santa Maria Valley. A more detailed description of the Santa Maria Project is contained in Chapter IV, Salinas Dam and Reservoir were constructed in 19hl by the U« S» Army to provide a water supply for Camp San Luis Obispo. Pertinent data -106- relating to Salinas Dam and Reservoir are included in the following tabulations Type of dams Concrete archo Height above stream beds 135 feeto Crest lengths I4.6O feeto Spillway crest elevations 1,301 feeto Spillway discharge capacity? 1*2,000 second-feet Initial reservoir storage capacity s 26,Oir3> acre-feet. Net safe seasonal yields 3> 5 600 acre-feet Capital costs $l,711*<,600o Water is conveyed from Salinas Dam through 1*8,700 feet of 2l*-inch diameter reinforced concrete pipe to a 3 5 000 , 000 gallon regulating reservoir at Santa Margarita booster pumping station The pipe line has a rated capacity of 12 oli second -feet under gravity flow from Salinas Reservoir when the reser- voir water surface is at an elevation of 1,267 feet. A booster pumping station at the dam,, consisting of two diesel-driven horizontal centrifugal pumps , is capable of maintaining the rated flow of 12 ol* second-feet when the water surface elevation falls below 1 5 267 feeto Three electrically driven horizontal centrifugal pumps are provided at Santa Margarita booster station which pump water through an additional 6 5 8l0 feet of 2l*-inch diameter reinforced concrete pipe to the entrance portal of Cuesta Tunnel,, a £ 9 32 7-foot, partially lined tunnel through the Santa Lucia Range, From the outlet portal of the tunnel, water is conveyed through an 18-inch diameter steel pipe line a distance of 5 5 700 feet to a bifurcation structure A pipe line from one branch of the bifurcation structure conveys water to the City of San Luis Obispo filtration plant located at elevation 5>£0 feeto Approximately 3 5 1*80 feet of 18- and 12- inch diameter steel pipe can convey water from the other branch of the bifurcation structure to Chorro Creek Reservoir and the filtration plant at -107- Camp San Luis 0bispo o Pertinent features of Chorro Creek Dam and Reservoir are presented in the following tabulation? Type of dams Earthfillo Height above stream beds 80 feeto Crest lengths £00 feeto Spillway crest elevations 610 feeto Initial storage capacity s 220 acre-feeto Net safe seasonal yields 5>0 acre-feeto Approximate capital costs $200^000 o The tributary drainage area above Salinas Reservoir is 111 square miles, and the mean seasonal inflow to the reservoir is estimated to be about 25*000 acre-feeto Based on reservoir operation studies conducted by the Division of Water Resources, the gross safe yield of the reservoir is estimated to be about 5,800 acre-feet per season However <> under the terms of the water right permit under which the project is operated, and which will be further discussed, stream flow entering the reservoir during the months from July through October must be released down the Salinas River to satisfy vested rights. On the basis of this latter requirement, the net safe seasonal yield of the reservoir is estimated to be 5 S 600 acre-feet. An agreement^, dated January 1, 19Ui, was entered into by the U S, Army and the City of San Luis Obispo providing for sale of a specified amount of water at a specified price for delivery at the bifurcation structure on the Salinas Reservoir conveyance conduits The agreement specified a term of one year with the further provision that the agreement will continue in effect for as long a time as no action is taken by the Secretary of the Army or the City to cancel ito The contract has been renewed from year to year with revisions of water rates and amounts of water deliveredo The most -108- recent version of the agreement provides for delivery at a maximum of 3*000 acre-feet per year at an average cost to the City of $72 per million gallons or about $22 per acre-footo An agreement., dated May I, 1952 s was entered into by the U c So Army and the San Luis Obispo County Flood Control and Water Conservation District, providing for the operation and maintenance of the Salinas Reservoir and con- veyance system by the District., The agreement also provided that the Army would reimburse the District for expenses incurred in the operation and mainte- nance of the project and directed the District to deliver water to any water service customers designated by the Army In compliance with specific requests by the City of Paso Robles and the towns of Santa Margarita and Templeton, the Army has on several occasions directed the San Luis Obispo County Flood Control and Water Conservation District to make releases from Salinas Reservoir It is reported that releases were made down the channel of Salinas River during the dry-weather portion of each year from 19U2 to 19U5 S with a live stream being maintained as far as Camp Roberts o Records of all of these releases., however, are not available. Set forth in Table 15 are the quantities of water diverted from Salinas Reservoir through its conveyance conduit to the Coastal Unit as well as quantities released down the Salinas River , to the extent of available information,, Quantities listed in Table 15 as releases are those in addition to the normal low flow summer releases required between July 1 and October 31 of each year under terms of existing water right permits Quantities listed as diversions in Table 15 are measured at Salinas Dam, -109- — TABLE 15 HISTORIC DIVERSIONS AND RELEASES FROM SALINAS RESERVOIR In Acre-Feet Season 9 g i October 1 - Septo 30 s Diversions s Releases i Total 19I|1-U2 50 1,1*60 1,510 U3 960 960 Wi 1,290 -— 1,290 19UU-U5 i,5io «.____ 1,510 k6 1,680 U,580 6,260 hi 2,020 2,830 M5o U8 2,320 ..... 2,320 U9 2,230 ..... 2,230 19U9-50 2,260 ..... 2,260 51 2,550 «,.«„_ 2,550 52 2,mo U,030 6,170 53 2,190 2,210 U,Uoo 5U 2 S 690 2,i|00 5,090 Water Service Agencies Water for urban and irrigation purposes in San Luis Obispo County is presently furnished by 2U water service agencies, 19 of which obtain their entire water supplies by pumping from ground water sources « Two agencies supplement their ground water supplies by surface diversions, and three agencies derive their entire supply from surface diversions <, The largest water service agency in San Luis Obispo County in terms of developed supply is the San Luis Obispo County Flood Control and Water Conservation District, which was formed by a special act of the State Legislature in 19h5° In addition to the San Luis Obispo County Flood Control and Water Conservation District, there are 25 organized water agencies within San Luis Obispo County including four municipal water departments, three private water =110= companies, eight mutual water companies, seven county water works districts, two county water districts, and one water conservation district <, Available data concerning the various agencies are summarized in Table 16^ including their approximate number of service connections and source of water supply. =111= TABLE 16 ORGANIZED WATER AGENCIES IN SAN LUIS OBISPO COUNTY, 1954 : Approximate s ; number of i Source s service s of [connections, i water supply Paso Robles Water Department 1,670 10 wells Atascadero Mutual Water Company 1^700 4 wells, one spring Garden Farms Mutual Water Company 50 1 well Green River Mutual Water Company 50 2 wells Atascadero County Water District none none San Luis Obispo County Water Works District No. 1- San Miguel 475 3 wells San Luis Obispo County Water Works District No„ 5 - Terapleton 189 3 wells San Luis Obispo County Water Works District No. 6 - Santa Margarita 170 3 wells San Luis Obispo County Flood Control and Water Conservation District 3 Salinas River Coastal Unit Arroyo Grande Water Department 1,200 3 wells Pismo Beach Water Department 1^.080 3 wells San Luis Obispo Water Department 5*600 Salinas River, Reservoir Canyon, 2 wells Avila Water Company 150 1 well Oceano Water Company 39 2 wells Los Osos Highlands Water Company 40 1 well Branch's Mill Water Company none Arroyo Grande Creek Cambria Pines Service Corporation 500 4 wells McNeill Pump Company none Arroyo Grande Creek Morro Rock View Mutual Water Company 180 1 well Paso Robles Beach Mutual Water Association 360 3 wells Grover City County Water District 1,030 2 wells San Luis Obispo County Water Works District No 2 - Morro Bay 1,200 3 wells San Luis Obispo County Water Works District No„ 4 - Morro Bay 510 2 wells San Luis Obispo County Water Works District No,, 8 «- Cayucos 180 2 wells ^112= ORGANIZED WATER AGENCIES IN SAN LUIS OBISPO COUNTY, 1954 (continued) : Approximate : number of Source % service of : connections, water supply 231 Coastal Unit (continued) San Luis Obispo County Water Works District No, 9 - Baywood Park 200 3 wells Santa Maria Unit Santa Maria Valley Water 300 wells Conservation District none -113- s • Appropriation of Water effective Since the date of the Water Commission Act of December 19 5 19l!i<> 77 applications to appropriate water of streams in San Luis Obispo County have been filed with the Division of Water Resources or its predecessors Applications filed through June 30c, 195>6 S are listed in Appendix G together with pertinent data on the proposed diversions and uses of water and present status of the applications* The applications listed in Appendix G should not be construed as comprising a complete or even a partial statement of water rights in the San Luis Obispo County area* They do not include appropriative rights initiated prior to December 19 5 1911i<> riparian rights 5 correlative rights of overlying owners in ground water basins 9 nor prescriptive rights which may have been established on either surface streams or underground basins s none of which are currently on record with the State Water Rights Board, In general,, water rights may only be firmly established by court decree. Water right permits covering storage and diversion of unappropriated waters of the Salinas River stored in Salinas Reservoir were issued to five agencies by the State Division of Water Resources as follows Storage Diversion Date of (acre -feet) (cfs) filing United States Army U5.000 12oU $-27-ai City of San Luis Obispo U5,ooo 12. k 6- U-lil City of Paso Robles 2,1*00 io-io-ia County Water Works District No, 6 (Santa Margarita) 200 1.5 2-26-1*7 County Water Works District No, 5> (Templeton) 200 1.5 £-28-1*8 It should be noted that the Army's permit is prior in time and right to all others listed in the foregoing tabulation e Downstream releases from Salinas Reservoir listed in Table 15> have been authorized by the Army when, -ill*- o in their opinion, sufficient water was available in the reservoir to meet prior rights Dams Under State Supervision The Department of Water Resources supervises the construction, en- largement, alteration, repair, maintenance, operation, and removal of dams, for the protection of life and property within California All dams in the State, excepting those under federal jurisdiction, are under the the juris- diction of the Department e As defined in the Water Code, "dam" means any artificial barrier, together with appurtenant works, if any, across a stream, watercourse, or natural drainage area, which does or may impound or divert water, and which either (a) is or will be 2$ or more feet in height from natural stream bed to crest of spillway, or (b) has or will have an impounding capacity of £0 or more acre-feet. Any such barrier, which is or will be not in excess of six feet in height, regardless of storage capacity, or which has or will have a storage capacity not in excess of l£ acre-feet, regardless of height, is not considered a dam The only completed dam currently under State supervision in San Luis Obispo County, other than the previously described Nacimiento Dam, is Atascadero Park Dam which impounds the waters of Atascadero Lake» As stated previously, Salinas and Chorro Dams are owned by the U» S. Army and are, therefore, not subject to State jurisdiction Atascadero Park Dam and Lake are owned by the County of San Luis Obispo and are operated as a recreational facility. The dam is an earthfill structure located on a small unnamed tributary of Atascadero Creek The dam is 17 feet in height and impounds some l£0 acre- feet of water In order to maintain the water surface of Atascadero Lake at the desired elevation for recreational purposes, supplemental water is -115- diverted to the lake from Atascadero Creek at a diversion point located about three miles upstream from Atascadero Land Us e For the purpose of estimating present water requirements in San Luis Obispo County 5 field surveys were made of the nature and extent of land use prevailing during the investigational seasons „ Also s in order to determine the probable ultimate water requirements of the County , field surveys were made to classify all lands in the County with regard to their suitability for various types of agriculture as well as for urban and suburban use<> Field surveys of land use and land classification were commenced in July,, 1953? and continued into August of 195>Uo Present Land Use As indicated previously 5 the only historical land use surveys within San Luis Obispo County for which maps and other supporting data are known to be available are those conducted by the U So Bureau of Reclamation and Division of Water Resources in 19U6 and 1950 5 respectively,, Utilizing aerial photographs taken of the investigational area in 19U9 and 1950 by the U„ S« Production and Marketing Administration,, a comprehensive land use survey was made in the field during the 1953-5U season as part of the current investiga- tion o All lands supporting irrigated agriculture and all urban lands were mapped during the survey o In addition,, on those lands overlying ground water bodies s all areas of phreatophytes and open water surfaces were mapped^ as well as fallow and idle lands equipped with irrigation facilities but not irrigated at the time of the survey All classes of nonirrigated agriculture and all areas of native vegetation on lands overlying ground water bodies were also mapped -116- To ascertain the extent of double and triple cropping in truck- cropped areas, four separate surveys of selected truck-cropped lands were con- ducted over a period of one year at three to four-month intervals © From the results of these special surveys , it was possible to determine the average acreage of truck-cropped lands actually under production in a given year as well as lands normally truck=cropped which are idle or lying fallowo Results of the 1953-5U land use survey showed a total of about 28,600 acres under irrigation in San Luis Obispo County and about 5,600 acres devoted to urban and military cantonment purposes© In order of total acreages 9 irri- gated crops include alfalfa, truck crops , permanent pasture, sugar beets, field corn, hay and grain, beans, cotton© and deciduous orchard© Field reconnaissance from time to time during the investigational seasons failed to disclose significant changes in the total acreage under irrigation or changes in the pattern of land use© Land use prevailing during the 1953-5U season is, therefore, taken as representative of "present" con- ditions of development throughout the County and investigational area and is so referred to in subsequent discussion,, Presented in Table 17 is a summary of present land use in San Luis Obispo County© Included under the heading, "Miscellaneous Field Crops", are sugar beets, field corn, beans and cotton Irrigated parks and golf courses are listed under the heading, "Urban and Military" © Military acreages listed under that heading include only the cantonment areas » All acreages presented are net water-using areas and do not include streets and roads© Farm lot inclusions in irrigated areas which were found to be largely nonirrigated were so classified© Irrigated farm lots, comprising less than one per cent of the total irrigated acreage are not presented in Table 17 as a separate category but rather are included in the acreages presented for the various crops© -117- o o o o o o cm un J- i OO H o HI fa O d ® Ti aj CN o at & fa O O Ol e- * • «t ^t-Jt CM in CM ON VOl «, •» oJ Hi unj-j o O O o vo Sn III fa so fa o o o VO OO CO Hi CM OO o o o o o o OO ir\ cm 3 UN .3- o 3 o o o 10 OO VO Jt o \o *• O o o & CO J- W <* fa O O Oi J- CM Hi I O O o o ON CO I"- CM • • ON £ 4-1 9 O O CM O H H) C«S «l 3 a -H fa O o o o w 60 CM ON CO ,J «T A! «9 PN UN VO UN O O. sa •a C\ C\ o fa fa H I o o 4r gj O CM 3 f^OO o O 1 O I CM t-~ 9 ON J* -3" £ O O Ol o o o o o vo co j* H en VO CO HI HI CM at «* o o o f^VO HI PNCO CM o O O UN CN UN OO O 3 SP ^ HI o •« fa c 1 o I *3 =118= Plates 11A 5 11B 5 and 11 C ? entitled "Present and Probable Ultimate Land Use'% show the areal extent of lands presently receiving water service in San Luis Obispo County Irrigated lands are shown in green and urban and suburban lands are shown in red„ A comparison of results of the land use survey made for this investi° gation with results of the 1950 survey show significant increases in the total acreage devoted to irrigated pasture and alfalfa An overfall increase in irrigated area of nearly 5 5 000 acres or 16 per cent was noted between 1950 and 1953 o Much of this increase has been due to the introduction of deep well turbine pumps enabling farmers to tap deeper aquifers of the Paso Robles Basin of the Upper Salinas Unit,, Irrigation development was previously limited generally to the relatively flat terraces and flood plains adjacent to streams However, development of sprinkler irrigation systems has enabled farmers to irrigate large acreages of rolling hill lands not heretofore considered suscep- tible of irrigation without costly levelingo These rolling hill lands are being devoted principally to pasture and alfalfa,. Truck farming has continued to be a major factor in the economy of San Luis Obispo County Approximately 9 S 500 acres, or nearly 33 per cent of the total County irrigated area,, are devoted to truck farming These truck cropped areas are located principally in the Santa Maria Unit and in the Arroyo Grande area in the southern portion of the Coastal Unit An average of 7 3 600 acres of land were truck cropped during the 1953-5U season Although most of the truck crop acreage reported for 1953 has developed on previously dry- farmed or native land, a portion of it has replaced previously irrigated deciduous orchards „ New plantings of sugar beets in the Upper Salinas Unit $ are meeting with general success. Cotton appears to be most successful in Cuyama Valley where prevailing temperatures are warmer at night and more =119- o favorable for its growth <, The County Farm Advisor and agricultural officials at California Polytechnic College report that unfavorable climatic conditions are the primary reason for the lack of commercial plantings of citrus orchards in San Luis Obispo County,, As previously stated, there are presently about 180,000 acres of land under dry-farmed crop production in San Luis Obispo County, including over 7,000 acres of almonds in the Upper Salinas Unit The bulk of dry-farmed grains are grown in the Upper Salinas and Carrizo Plain Units o Dry-farmed grain lands are usually fallowed and cropped in alternate yearso Probable Ultimate Pattern o f Land Use The economy of San Luis Obispo County is and always has been based primarily on its agricultural development, including extensive dry-farmed crop and beef production^. Except for growth resulting from the establishment of military reservations , urban growth as indicated by population figures has apparently paralleled that of agriculture.) Under ultimate conditions of development, it is reasonable to assume that this relationship will continue to prevail in most areas of the County e It is anticipated, however, that irrigation development will be of greater importance under future economic conditions,. Along the coastal strip north of Arroyo Grande Valley, favorable climatic conditions and a natural scenic beauty have encouraged the "resort" type of urban and suburban development© Increased growth of this type is anticipated in the future Because of the direct relationship between land use and water re- quirements, particular attention was given to the classification of lands within San Luis Obispo County suitable for irrigation and urban and suburban development and to the forecast of probable ultimate crop and urban land use -120- „ patterns,, A detailed land classification survey was conducted throughout the investigational area in the summer and fall of 195>U for the purpose of deter- mining the location and extent of lands suitable for irrigation development To assist in forecasting the ultimate crop pattern that would result from such development , lands were mapped in the field according to various crop adapta- bility classes o In so doing,, consideration was given to such physical charac- teristics as topography, soil depth, soil texture, saline or alkaline conditions, moisture holding capacity, high water table conditions, and the presence of rock. The projection of probable crop patterns on the various adaptability classes required consideration of climatic conditions, ease of irrigation, and current agricultural practices » No consideration was given to economic factors pertaining to the production and marketing of crops such as cost of water, cost of labor, available markets, and market prices, etc, as these factors are subject to wide variation over a period of years, and their relation to crop values may be considerably changed under conditions of ultimate develop- ment o Presented in Table 18 are descriptions of the various crop adaptability classes and standards used in the survey,. -121- , TABLE 18 LAND CLASSIFICATION STANDARDS Class ' Characteristics V Smooth lying valley lands with slopes up to six per cent in general gradient in reasonably large-sized bodies sloping in the same planej or slightly undulating lands which are less than four per cent in general gradient <> The soils have medium to deep effective root zones are permeable throughout, and free of salinity, alkalinity, rock, or other conditions which would limit the crop adaptability of the land. These lands would be suitable for all climatically adapted crops., Vp Similar in all respects to Class V, except for the depth of the effective root zone which limits its use only to shallow-rooted crops, such as grain and pasture. Vr Similar in all respects to Class V, except for the presence of rock on the surface or within the plow zone in sufficient quantity to prevent the use of the land for cultivated crops. These lands are suitable for the production of irrigated pasture crops VT Similar in all respects to Class V, except for having fairly coarse textures and low moisture holding capacities, which, in general, make these lands unsuited for the production of shallow-rooted crops because of the frequency of irrigations required to supply the water needs of such crops. Vw Similar in all respects to Class V, except for the present existing condition of a high water table which, in effect, limits the crop adaptability of those lands to pasture crops. Project drainage and a change in irrigation practices would be required to affect the crop adaptability of these lands. For the purpose of this investiga- tion, it is assumed that there will be no change in the use of these lands. Vs Similar in all respects to Class V, except for the presence of saline and alkali salts which limit the present adaptability of these lands to crops tolerant of those conditions. The presence of salts within the soil indicate poor drainage and a medium to high water table* The reclamation of these lands will require drainage and the applica- tion of additional water over and above crop requirements in order to leach out the harmful salts. Vm This class covers marshlands which under present conditions are non- irrigable, being under water a large part of the year. The present vegetation is mostly tules and water-loving types of plants. These lands would require extensive drainage before they could be utilized for agricultural crops. It is assumed that there will be no change, and that their water use will continue to be the same as the present. If this type of land were developed, the probable result would be a decrease in its water requirement. -122- LAND CLASSIFICATION STANDARDS (continued) Class ° Characteristics Va Land at present considered nonirrigable due to the presence of saline and alkali salts in excess of agricultural crop tolerance , The feasibility of reclamation of this type of land is presently unknown. It is* therefore, assumed for this bulletin that the ultimate land use of these lands will remain unchangedo H Undulating and rolling lands up to 20 per cent maximum slope for large-sized bodies sloping in the same plane, grading down to less than 12 per cent for undulating lands. The soils are permeable s with medium to deep effective root zones, and are suitable for the production of all climatically adapted crops. The only limitation is that imposed by topographic conditions which affect the ease of irrigation and the amount of land that might ultimately be developed,, Hp Similar in all respects to Class H, except for the depth of the effective root zone., which limits the use of this land to shallow- rooted crops, Hr Similar in all respects to Class H, except for the presence of rock on the surface or within the plow zone in sufficient quantity to restrict the use of the land to noncultivated crops, HI Similar in all respects to Class H e except for having fairly coarse textures and low moisture holding capacities which in general makes these lands unsuited for the production of shallow-rooted crops because of the frequency of irrigations required to supply the water needs of such crops, Hpr Similar in all respects to Class H, except for the depth of the effective root zone and presence of rock on the surface or within the root zone in sufficient quantity to restrict the use of the land to noncultivated crops, Ht Similar in all respects to Class H, except for topographic limita- tions. These lands have smooth slopes up to 30 per cent in general gradient for large-sized bodies sloping in the same plane, and up to 12 per cent slopes for rougher and more undulating topography. This class of land will not be as highly developed as other MH" classes of land and is considered as best suited only for irrigated pasture land, Htp Similar in all respects to Class Ht ? except for the depth of the effective root zone 3 which limits the use of this land to shallow- rooted crops. »123- » LAND CLASSIFICATION STANDARDS (continued) Class Characteristics Htr Similar in all respects to Class Ht, except for the presence of rock on the surface or within the plow zone in sufficient quantity to restrict the use of land to noncultivated crops Htl Similar in all respects to Class Ht 5 except for having fairly coarse textures and low moisture holding capacities., which, in general, makes these lands unsuited for the production of shallow-rooted crops because of the frequency of irrigations required to supply the water needs of such crops, Htpr Similar in all respects to Class Ht, except for the depth of the effective root zone and the presence of rock on the surface or within the root zone, which limits the use of these lands to noncultivated shallow-rooted crops N Includes all lands which fail to meet the minimum requirements of the foregoing classeso -12U- In addition to those lands considered to be potentially irrigable, as defined by the foregoing standards, certain lands, by virtue of their topographic characteristics and proximity to either existing urban centers or probable future urban areas, were considered susceptible to urban and suburban development o These lands, though in some cases possessing all of the necessary characteristics of irrigable lands, were not so classified and are termed herein as "habitable areas "o Results of the county -wide survey show there are about 31>000 acres of land considered to be habitable under this definition,. Approximately four per cent, or 1,100 acres of lands classed as habitable, are presently irrigatedo Results of the land classification survey show that there are about 1^11,000 acres of irrigable lands within San Luis Obispo County,. About 38 per cent or 155,000 acres of irrigable lands within the County are relatively flat "valley lands" comprising flood plains and terraces., Over 30 per cent of these lands are found within the Carrizo Plain Unit with large acreages also in the Salinas, Cholame, and Estrella Valleys of the Upper Salinas Unit, About 116,000 acres of irrigable valley lands have adequate soil depths and are suitable for the production of all climatically suited crops with most types of irrigation practice o The remainder of irrigable valley lands, because of limiting soil depths, are generally suitable for the production of irrigated grain or pasture About 256,000 acres of hill lands are classified as irrigable,, These lands, comprising 62 per cent of the gross irrigable area within the County, and typified by relatively steep or rolling topography, generally will require special irrigation practice. Approximately 102,000 acres of these lands in the County, classified as Class "H", have fairly deep and well developed soil profiles and are suitable for all climatically adapted »125- crops. Large acreages of irrigated pasture are currently being developed on these lands<, Nearly 38 per cent of the gross irrigable area, or about 15U>000 acres, comprise the remainder of irrigable hill lands in the County which, because of excessive slopes, shallow soil depths, or presence of rock, are suitable for the development of irrigated pasture only These lands are found scattered throughout all hydrologic units . Results of the land classi- fication survey of San Luis Obispo County are summarized by units and subunits in Table 19« -126- 1 o o o o o O o 8 o o o o 8 o o a« o% CT> c\ °\ o\ o\> ON OJ in CO H -3- On QO On in NO r>- in CM Os -3" CM CM H 02 o\ H CM CO OOOI p o o o o o o o Eh Oj oi o« cohhh|c— cnl oo oo o O o o o o o vO CO c^ On f>- _=r H -3- en CM -3- o H CO CD <*> o\ «\ "V o« o» o» _^r H o On vO H On H c>- m ,o en H en en -d" in H HOn CO CO CO -=T CM H C>- •h a H o\ U CO OOOI M Sh H enm evi E-i H o\ino\ 3 ri at «% *y Jo O co m-=n O s vo-^-o o H H H| o cu oo oo CO O O o O O o 1 ° H • -J- hi 03 ! p O O Oj CD o-o-co P % o co O^ <% o>J CO < H mCM| On 2 c H H buni P nit Top p p CO S -P co ,g CO P H Eh •POMp oo EHH O P •H ft EH |3 Eh •H ,Q :=> q to cd o\ H J3 bO p 3.HTJ CO y O CO t3 „ -2:9 e s H S3 En P O S™ ^ O T3 s H CO *h •p «< EH ^ s ^Q co { ! (_j ^ a M s o o f— — fc} H p CO U p Ph 1=3 >4 3 Lui ,o % g o Eh bria m CO AL oyo p s O ^ O CO *a^ e survey , and information gathered from other available sources s a probable ultimate pattern of land use as related to water requirements, was developed for the investigational area* Estimates of water requirements for irrigated agriculture are based, in part, on the net number of acres of land which will be irrigated during any one season^ Net acreages were computed by the applica- tion of appropriate percentage factors to gross acreages as derived from the land classification survey,. The foregoing factors accounted for the effects of the size and shape of the parcels of irrigable lands, inclusion of small areas of nonirrigable lands among those classified generally as irrigable^ productive capacity of the lands and probable crop rotation, ease of irrigation development, and inclusion of roads, railroad rights of way, and other non- agricultural land uses© The factors were largely based upon experience and judgment of the classifiers, supplemented by consultation with residents and agricultural officials of the investigational area, and knowledge of the characteristics of the lands under considerati on e The probable ultimate pattern of land use was projected utilizing the net irrigable acreages derived from the land classification survey and by consideration of climatic conditions, present land use pattern, and present trends in the development of irrigated lando It has been estimated that the predominant irrigated crops under ultimate conditions of development will be pasture, alfalfa, and trucko It is anticipated that the local cattle industry will increase in valuation with a greater proportion of the animals being raised on permanent pasture 9 Demand will increase for supplemental feed, and proportional increases have been projected for irrigated hay and grain* -128« It is assumed that irrigation will eventually be applied to presently dry-farmed deciduous orchards and vineyards. New acreages of these crops will be developed on presently native or dry-farmed lands. It is expected that new markets for truck and field crops will develop as the State and local population increases , and appropriate allowance has been made for these crops in the ultimate crop pattern Recent increased urban and suburban development in lower Arroyo Grande Valley and along the coast from Morro Bay north, represents a trend of development which,, it is estimated^, will ultimately encompass about one -third of the habitable lands within the Coastal Unit, Improvement of State Highway No, 1 and construction of its proposed extension south of Morro Bay along the coast will also provide impetus to urban and suburban development along the entire coast line© From analyses of historical population records and miscellaneous agricultural records , it has been assumed that future urban growth will be proportional to future growth of irrigated agriculture in the Upper Salinas Unit, As discussed hereinbefore, it appears that urban and suburban develop- ment will be proportionally larger in the Coastal Unit, This assumption appears valid in view of the extent of lands presently zoned for residential,, commercial , and industrial activity and is supported by future zoning plans currently being developed by the staff of the County Planning Commissiono In the Santa Maria and Cuyama Units 3 it is not expected that urban and suburban growth will parallel agricultural growth, as urban centers supporting those units are and probably will continue to be located in Santa Barbara County, Under ultimate conditions of development in the Carrizo Plain Unit, it is assumed that lands will remain in relatively large holdings as at present, and that most of the urban and suburban development serving that Unit will =129- continue to be located outside of the Unite For the foregoing cited reasons, urban and suburban development in the Santa Maria, Cuyama, and Carrizo Plain Units has been expanded to a much less extent , percentagewise , than in the Upper Salinas Unit* Because of its remote location, no urban development appears likely in the San Joaquin Unito Based on the foregoing assumptions, it is estimated that about 297,000 acres of land will be irrigated under ultimate conditions of develop- ment and water use* It is further estimated that about 36,000 acres of urban and suburban lands will ultimately require water service „ Presented in Table 20 is a tabulation of estimated probable ultimate water service areas in San Luis Obispo County summarized by units and subunits<> Irrigable and habitable lands, as determined by the land classification and habitable area surveys, are shown on Plate 11, where, for illustrative purposes, differ- entiation has been made between valley and hill lands as tabulated in Table 19. Although no differentiation has been made between irrigable and habitable lands shown on Plate 11, it is probable that future urban and suburban development will occur in the vicinity of present urban areas with development of present vacant inclusions and peripheral lands taking place firsto For the purpose of this bulletin, it is assumed that no further increase or decrease will take place in military cantonment areas -130= O o o o O o o H O 1-1 o o> 8 * * MS o H So O OS o> ©> Oi Oh • Oh ti) .h a) t>^ o us SO O CM CS 5 HI O O Ol fv H CM o en o rt £ fa HI H en E- S >* O o o O o 1 o c» o o o o o o H o M OO CM us OO 0) Ch •*= 5 o o J" *» .o 3 CO CO o col CM o O o o o o o O a OO HI CM J- OO Cn >,T3 -rf Ch cd c «S C-. K a} fa VO W) o o O o o o o o O HI CO o o t^. o t3 (0 O HI A B C O «H «H fa a <^ © W < O E- • > *• o o o o o O en O IB P| o o o o o O w O a> o o H o CM to fa 'J o o O P ° o O O I o a. < >-.: fa fa O O o CM g to E-* O J- 4>-0 e- M c as Ch o w «< CQ •H 1 hi en so J 3= O m U -Ci 4j < M 10 fa o O I o E- E- M $ o O I O «aj » fa a? ft US MS I a J -* ^ • g •X a E- 4» fa •H 5 CO fa g H .. *?. T3 o o o o i 1 1 o -1 s fa o o o g i j o CQ ir\ CM en 1 I MS << CQ p o o o O fa o o o 02 o HI CM CM a. o o o o o o o HI HI o « OS 15 OO o en Oh Ok 31 • O ON +» o o HI H 3 ON 01 OO O 3 J- J- o3 CL. +> -131- o $ Unit Use of Water The second step in evaluation of present and probable ultimate water requirements of San Luis Obispo County involved the determination of appro- priate unit values of water use for each class of land requiring water service. Use of water was also determined for certain classes of native vegetation and dry-farmed crops, as required , for purposes of hydrologic analysis,, Unit Values of Consumptive Use For the purpose of supplementing available consumptive use data and to provide additional data in support of estimates of water requirements, a program of soil moisture depletion studies was conducted at representative irrigated, dry-farmed, and native vegetation plots during the 1953-5U growing season Soil moisture depletion studies consisted of both field and labora- tory work and involved (l) the collection of soil samples from representative plots at specified intervals of time prior to and following irrigations, (2) determination of both field and oven-dry weights of the soil samples (3) reduction of resultant values of contained moisture to equivalent inches depth of water, and (3) determination of rates of consumptive use of water during intervals of time between successive samplings » Detailed results of all soil moisture depletion studies, including methods and procedures utilized therein, are presented in Appendix K„ Descriptions of investigational test plots are included in the appendix, and their locations are indicated on Plate 11 Unit values of consumptive use for various crops were computed for each of the units and subunits of the investigational area using a procedure suggested by Harry F„ Blaney and Wayne Do Criddle, of the Soil Conservation -132- 5 Service,, United States Department of Agriculture, in their reports entitled "A Method of Estimating Water Requirements in Irrigated Areas from Climatology ical Data" dated December, 19U7, and "Determining Water Requirements in Irrigated Areas from Climatological and Irrigation Data", dated August, 19^0. The method as described in the latter report is as follows; "Briefly, the procedure is to correlate existing consumptive use data with monthly temperature , monthly percentages of yearly daytime hours 5 precipitation,, and growing or irrigation season use Coefficients have been developed from existing measured consumptive use and temperature data and monthly percents of year- ly daytime hours Thus if only monthly temperature records are available and latitude is known, the consumptive use can be com- puted from the formula U-KF^ where U - consumptive use of water in inches for any period, K = empirical consumptive use coefficient, and F - sum of the monthly consumptive use factors for the period (sum of the products of mean monthly temperature and monthly percent of annual daytime hours) " As can be seen from the foregoing description, no direct consider- ation is given to the effect of wind movement, fog, and humidity on the rate of water consumption,, These factors are generally unmeasured and the few available records thereof are usually of relatively short length in comparison to other available climatological data Effects of the foregoing variables are believed to be largely responsible for the differences in the quantity of water consumptively used by certain crops grown under otherwise identical climatological and other environmental conditions o As shown in Appendix H, "K" factors derived from soil moisture depletion studies conducted in San Luis Obispo County varied by as much as 20 per cent, depending upon the crop and hydro graphic unito The following is an outline of the procedure utilized in estimating unit values of consumptive use for San Luis Obispo County lo Measured growing season units of consumptive use of water as derived from soil moisture depletion studies were employed in the cited -133- « formula for the purpose of computing appropriate consumptive use coefficients for the particular investigational seasom The coefficient (K) was derived as the quotient of the measured growing period consumptive use of water (U), and the consumptive use factor (F)« The available heat or consumptive use factor in this step was taken as the sum of the products of the average monthly temperatures prevailing during the 1953 growing season and the monthly percent of annual daytime hours at the location of the plot 2 Average consumptive use coefficients were then computed for each crop studied,, For those crops included in the present and probable ultimate pattern of land use which are not grown presently or for which suitable study plots could not be found, results of similar studies in other areas were utilized by correlation with local climatological conditions 3e In a given subunit*, the unit value of consumptive use of water for each irrigated crop during its growing season was taken as the product of the weighted 16-year base period average consumptive use factor for the sub- unit and the appropriate coefficient of consumption, derived as in (l) above, ko Unit values of consumptive use of water for each crop during the nongrowing season were taken as the amount of precipitation available, up to but not exceeding one or two inches of depth per month, depending on the crop $ The total seasonal unit value of consumptive use of water for each irrigated crop was then taken as the summation of values derived under items (3) and (U)« 60 That portion of the unit seasonal value of consumptive use of water supplied by precipitation, termed "effective precipitation", was taken as equal to the sum of water consumed during the nongrowing season, consump- tive use of direct precipitation occurring during the growing season, and -13U- o „ „ consumptive use of moisture stored in the soil during the nongrowing season but utilized during the growing season,, 7o Unit values of consumptive use of applied water for each irrigated crop were taken to be the difference between total seasonal consumptive use of water and effective precipitation,, 8 Unit seasonal values of consumptive use of water for grain and other dry-farmed crops were based on rates of consumptive use observed at study plots in connection with the soil moisture depletion study and on data gathered in connection with similar studies elsewhere,, 9o Unit seasonal values for native annual grasses were taken as the summation of available precipitation up to 5 but not exceeding^ two inches in depth per month 10 o Unit seasonal values for native vegetation other than native annual grasses were estimated from available data modified so as to apply to local conditions of water supply and climateo llo Unit seasonal values for free water surfaces were estimated from records of evaporation at Salinas Reservoir and available temperature records 12 Unit seasonal values of consumptive use of water by various categories of urban land use were estimated from comprehensive data gathered in a previous study by the Division of Water Resources in the Los Angeles Metropolitan Area The reasonableness of these units as applied to local con- ditions was checked by application of the units to selected water service areas for which water production and land use data were available Estimated unit mean seasonal values of consumptive use of applied water 5 effective precipitation,, and total seasonal consumptive use of water on irrigated and urban lands in the investigational area under both present -135» « and ultimate conditions of development are presented in Table 21 » Unit values contained in Table 21 are also considered representative of average values pre- vailing during the base period. For illustrative purposes, the monthly distri- bution of mean seasonal consumptive use of water by alfalfa and truck crops in the San Luis Obispo and Shandon areas is depicted on Plate 12, entitled "Monthly Distribution of Mean Seasonal Consumptive Use of Water by Representa- tive Crops, San Luis Obispo County" -136- HI 1 (A (H <3 CO J- s» (a 0) ¥> W !0 ttj P•'> a c P^ C\CM »» E- © o •.-I . o * S > rt to o -:- 1 •0 G «3| C •• .' & t c cu o •i-l W .w fMN I I lit i 1 •*» O O CO 3 a • oil Oil 1 I o o o 6 0© e © O O HI HI rJ H O O H O o3 £^ c •o a ® &. w —i e HI rt H) c\co IflO CM c=a*>» H) +> o o c o o o o o o C^C^\ CM CM O gig • a • *> . - ii - a. H oj 9 S 3 o\ ©\ tr\ o ie\ trsjf U>CM O to m o o o I o « © o © o o o o SP 1o a c t»Acr\CM CM CM HI OCN 0=1 W N pi «r3 E- o o H C IS o v^ c Hi 1 • a) a. i-t c s 3 o 3 UMt\C^VO J- CM OJ PNirx VO-* 4? • a e e « 9 © 4 o 3 g C^C1^ CM H CM CM Hi E- 4> o H ro a ;.' P t •««. "j" H) I fi. •-» c a B lf\ C\ o 3 c\e»\co 11 ^t Hi O C\ ITS a © © • o o o o m us • o © e I ©00 o C\C\CM f-3 CM CM 5=3 1 1° i C > C^N C^ H c«l CM H HI H -PiE- 4E> O «4 vlU CO O ^' & 1 a) o. o o r=3 Hi •H tH HI HI HI g ffvplls o o o o \a t^t^. ^J o © o o o e o M (j cool ©00 H HI H OHO O o 1 l 41 $\" oc «« M a 3 \£> i«s. C*\ t^J- cn IT\ \0 CO w CM CM IS- ( UNO C\ VO CO +» o o 9 o o o o o o o e HI fl OOO O O CM CM O o-» H O O O H) • us to 3 •a 3 § TO Q HI h 4-4 I 13 £» O "137- Units of Applied Water Studies were made of the amounts of water applied to typical irrigated crops in San Luis Obispo County during the 1953 and 195U irrigation seasons. Results of these studies, supplemented by the results of previously described water use studies, provided sufficient bases for the estimation of mean seasonal units of applied water for irrigated and urban lands under both present and ultimate conditions of development*, During the course of the field investigation, measurements were made of the amount of water applied to 27 test plots of representative crops, including alfalfa, pasture, walnuts, sugar beets, artichokes, celery, and lettuce 8 Test plots were selected so as to include typical soil types mapped in the land classification survey. For each plot, data were recorded as to the area irrigated, frequency of irrigation, and the amount of water applied. Applied water was computed from records of power consumption maintained by cooperators and Division of Water Resources personnel, and from pump test reports provided by Pacific Gas and Electric Company. Results of applied water studies indicate a wide variation in irrigation practice with respect to both frequency and quantity of water application. Major factors contributing to these differences include differ- ences in crops, climate, soil types, method of irrigation, and the skill of the irrigator. Climatic variations were found to be the major cause for seasonal differences in applied water at individual plots. All of these variations are typical of most irrigated areas and can be expected to occur in the future. Similar variations can be expected in urban and suburban areas, although not to such a marked degree. A summary of the results of applied irrigation water studies in San Luis Obispo County is presented in Table 22. Detailed results of those -138- — studies are presented in Appendix H< TABLE 22 MEASURED AVERAGE SEASONAL APPLICATION OF IRRIGATION WATER ON REPRESENTATIVE CROPS IN SAN LUIS OBISPO COUNTY Applied water Number of plots in feet of depth : Weighted Unit j average 1953 s 195U : Total 195U ' for two : seasons UPPER SALINAS UNIT Alfalfa h 2 6 U.o 2.6 1.5 Pasture k h 8 U.7 3.5 U.l Field corn - 1 1 — — 1.9 1.9 COASTAL UNIT Alfalfa - 1 1 2o5 2.5 Pasture - 1 1 ___ 2.U 2oU Walnuts - 1 1 io5 1.5 Sugar beets l 1 2 1.0 l.l l.l Artichoke sa i 2 3 1.1 0o7 o 8 Celerya 3 - 3 U.O U.o Lettuce = 1 1 0.7 0.7 a Single crops, three and four month irrigation seasons. b Single crop, three month irrigation season. Irrigation efficiencies derived from data presented in Table 22 and from the results of soil moisture depletion studies were used as bases for the computation of mean seasonal units of applied water under both present and ultimate conditions of development and water use. Defined as the ratio of consumptive use of applied water to the total applied water, irrigation efficiency is commonly expressed as a percentage. Results of studies in San Luis Obispo County indicate a variation in irrigation efficiency under present conditions ranging from 3U to 90 per cent. Although irrigation efficiencies vary widely between crops and among -139- plots devoted to the same crop, it is felt that irrigation efficiencies currently being achieved in San Luis Obispo County are somewhat lower than those being achieved in other areas wherein irrigation has been practiced longer o With the exception of truck and field crop irrigation in the Coastal and Santa Maria Units, the vast majority of lands presently under irrigation in San Luis Obispo County have been developed since the end of World War II. As would be expected, considerable variation in irrigation technique exists and will continue to exist as farmers refine their procedures and develop more efficient systems. In a report by the United States Soil Conservation Service entitled "Ground Water Replenishment by Penetration of Rainfall, Irrigation, and Water Spreading in Zone 3, Ventura County Flood Control District, California", dated April, 1953$ it was indicated that for the area studied, efficiencies of 7U to 77 per cent prevailed for alfalfa and irrigated pasture, 58 to 6k per cent for beans, and 70 to 75 per cent for summer truck crops* High efficiencies are difficult to achieve in all instances because of differ- ences in root depth, soil type, topography, method of irrigation, drainage characteristics, and in the practices of the individual irrigators, but it is believed that over a period of time, as techniques are developed and refined, irrigation efficiencies within San Luis Obispo County will generally improve. Records of irrigation efficiencies in Ventura County, where irrigation has been practiced for a relatively greater number of years, are considered indicative of efficiencies which could be achieved in San Luis Obispo County. Presented in Table 23, are irrigation efficiencies considered to be applicable to San Luis Obispo County for both present and probable ultimate conditions of development -1U0- _ TABLE 23 ESTIMATED IRRIGATION EFFICIENCIES UNDER PRESENT AND PROBABLE ULTIMATE CONDITIONS OF DEVELOPMENT IN SAN LUIS OBISPO COUNTY s Irrigation efficiency Crop s Present : Ultimate Alfalfa 50 6$ Pasture 50 6$ Orchard 75 80 Truck 75 80 Miscellaneous 75 80 Hay and grain 75 80 Vineyard _ 65 For illustrative purposes , there are presented in Table 2U estimated mean seasonal units of applied water for each of the units and subunits in San Luis Obispo County applicable to present conditions of development,, Modified versions of present irrigation efficiencies, reflecting anticipated future changes in irrigation practice^ were used to derive units of applied water for ultimate conditions of water use Variations in weighted units of use for urban, suburban, and military lands appearing in Table 2k reflect differences in prevailing patterns of development rather than actual differ- ences in estimated unit use of water -llil- — - TABLE 2k ESTIMATED MEAN SEASONAL UNITS OF APPLIED WATER IN SAN LUIS OBISPO COUNTY UNDER PRESENT CONDITIONS OF DEVELOPMENT In Feet of Depth • : Urban, • e Irrigated agriculture : suburban, e « « Hydrologic unit • * 4 « • : and * « and subunit • s Truck sMis c<>: Hay :military, lfalfa : Pasture: Orchard : crops: field: and : weighted • * : : crops: grain : average UPPER SALINAS UNIT 5»2 5oU 1.7 1.9 lo7 0.7 3o2 COASTAL UNIT Cambria Subunit 3.2 I|o0 0.8 O 7 0.1 3.1 San Luis Obispo Subunit li 6 0„9 2,0 1.1 0.1 3.0 Arroyo Grande Subunit llo2 Uo6 1.1 2o0 lc3 0o3 2.8 SANTA MARIA UNIT k-h k*h _-- 2.3 2.0 3.0 CUYAMA UNIT 5»6 5o6 ___ — 2*0 0.7 — -„- „~_ CARRIZO PLAIN UNIT 6 a ii 6.k 2.1 0.9 — SAN JOAQUIN UNIT — ... ~__ -11*2- , Unit values of applied water for ultimate conditions of development corresponding to those presented in Table 21+ were derived similarly. The ultimate values , reflecting higher irrigation efficiencies, varied from 77 to 9k per cent of the values presented in Table 2lu No change was forecast for urban and suburban units of applied water as it is believed that any such change will be negligible. Water Requirements Water requirements in San Luis Obispo County under present and probable ultimate conditions of development were estimated by multiplying the acreage of each category of land use under present and probable ultimate conditions of development by appropriate units of water use with due consider- ation given to geologic conditions affecting the use and re-use of water e In portions of the County wherein water applied to lands in excess of consumptive use will either return to ground water storage and be available for re-use or will drain from the area under consideration and be available for re-use downstream, the measure of water requirement was taken as the amount of con- sumptive use of applied water For lands overlying confined ground water bodies, wherein it was assumed that water applied in excess of consumptive use is prevented from returning to ground water storage for subsequent re-use, or in those areas wherein the unconsumed residuum drains directly to the ocean or is otherwise unavailable for re-use, the measure of water requirement was taken as the amount of applied water e Both present and ultimate seasonal water requirements for irrigated lands were evaluated for conditions of water supply and climate that would prevail with a repetition of climatic conditions which occurred during the base period. Requirements so estimated were taken as equivalent to mean -1U3- seasonal water requirements under the two conditions of development. Present Water Requirements Based on the foregoing criteria, the present mean seasonal water requirement of San Luis Obispo County was estimated to be about 69,000 acre- feet . Except for portions of the Coastal and Santa Maria Units wherein excess applied water drains directly to the ocean ' or is discharged thereto as sewage effluent, present water requirements for all other areas of San Luis Obispo County were estimated utilizing unit values of consumptive use of applied water. Urbanized areas of the Coastal Unit, wherein total applied water is considered the measure of demand under present conditions of development, include the Cayucos-Morro Bay, Avila, Shell Beach, and Pismo Beach areas. The determination of water requirements within military reservations for any particular period is inherently difficult because of changing inter- national conditions affecting their position in the military preparedness program. Past history of the operation of the two military reservations within San Luis Obispo County have indicated a widely fluctuating water demand. In addition to their use during World War II, when their demand for water was perhaps at a peak, both reservations have been or are being used periodically for U. S. Army Reserve or National Guard training purposes during the summer months. The hospital area of Camp San Luis Obispo is presently being utilized as a medical facility of the State of California, Department of Corrections. For the purposes of this report, estimates of present water requirements for the cantonment areas in military reservations have been based upon the assumption of maximum utilization of the area for military purposes. In the absence of complete records of water use at the two camps during World War II, an attempt was made to estimate such use by the application of appropriate -lUii- units of water use to the various prevailing categories of land use« Water requirements for irrigation purposes in national forest areas or military reservations outside of cantonment areas are included in total water require- ments hereinafter presented., Presented in Table 25 5 are estimated present mean seasonal water requirements for San Luis Obispo County by units and subunits derived on the basis of the afore~mentioned methods and assumptions. TABLE 25 ESTIMATED PRESENT MEAN SEASONAL WATER REQUIREMENTS IN SAN LUIS OBISPO COUNTY In Acre-Feet Irrigated sUrban, suburban,? Hydrologic unit and subunit agriculture t and military t Total UPPER SALINAS UNIT 26^000 900 26,900 COASTAL UNIT Cambria Subunit 1,100 100 1,200 San Luis Obispo Subunit Ii,5oo 3,800 8,300 Arroyo Grande Subunit 5,800 900 6,700 Subtotals s Coastal Unit 11,1*00 U,800 16,200 SANTA MARIA UNIT 16,600 16,600 CUYAMA UNIT 8,200 8,200 CARRIZO PLAIN UNIT 600 600 SAN JOAQUIN UNIT TOTALS 62,800 5,700 68,500 Probable Ultima te Water Requirements Water requirements in San Luis Obispo County, under probable ultimate conditions of development, were determined by multiplying the estimated 1U5- » acreage of each type of land use by appropriate unit values of seasonal water use with proper consideration given to anticipated future conditions affecting the use and re-use of water o Accordingly , the probable ultimate water require- ment of San Luis Obispo County is estimated to be approximately 721,000 acre- feet per season As in the case of present water requirements, estimated ultimate water requirements for Upper Salinas, Cuyama, and San Joaquin Units were de- rived from units of consumptive use of applied water » Under ultimate con- ditions of development^, it was assumed that urban and military development in the Coastal Unit would be served by sewerage works discharging their effluent directly to the ocean» The measure of demand for areas so served was, there- fore, assumed to be the total applied water as was the case for irrigable lands which drain directly to the ocean or which overlie a confined ground water basin» In the Santa Maria Unit, total applied water was taken as the measure of demand for irrigable and potential urban lands overlying the con- fined ground water body in the western part of the Basin For all other irrigable and potentially urban lands within the Unit, estimates of ultimate water requirements were based upon unit values of consumptive use of applied water As discussed previously, geologic and topographic evidence indicate that little if any re-use of return irrigation flow will be effected in the Carrizo Plain Unit under ultimate conditions of development* Furthermore, it appears that a large body of water would form at Soda Lake from pondage of return irrigation flow, unless suitable artificial drainage facilities are provided,. Without such measures, it was estimated that evaporation from the lake would approximate 15*000 acre-feet per season, with conditions of -1U6- o development and water use proposed herein^ before the lake would become stabilized,, A stabilized condition would be reached when net evaporation from the lake would be just equal to the total return irrigation flow<, It is therefore believed that total applied water will be the measure of demand in the Carrizo Plain Unit under ultimate conditions of developments This assumption would be valid regardless of the crop pattern or any measures which would be undertaken to alleviate the drainage problem,, Estimates of probable ultimate water requirements for lands on military reservations were based on the assumption that present cantonment areas would undergo no further expansion and that irrigable lands would be irrigated to the maximum practicable extento Ultimate water requirements for cantonment areas were derived by the same method as were the present water requirements A summary of estimated probable ultimate mean seasonal water re- quirements for 'the various units and subunits within San Luis Obispo County 3 derived in accordance with the afore-mentioned methods and assumptions, is contained in Table 26 -11*7- TABLE 26 ESTIMATED PROBABLE ULTIMATE MEAN SEASONAL WATER REQUIREMENTS IN SAN LUIS OBISPO COUNTY In Acre-Feet Irrigated :Urban, suburban,: Hydrologic unit and subunit agriculture ; and military : Total UPPER SALINAS UNIT 212,800 8,200 221,000 COASTAL UNIT Cambria Subunit 15 , 300 6,,900 22,200 San Luis Obispo Subunit 37,U0O 39,,800 77,200 Arroyo Grande Subunit 33,200 23,,600 56,800 Subtotals, Coastal Unit 85,900 70,300 156,200 SANTA MARIA UNIT 26,700 800 27,500 CUYAMA UNIT 62,800 I4OO 63,200 CAREEZO PLAIN UNIT 212,800 3,200 2ii6,000 SAN JOAQUIN UNIT 7,200 7,200 TOTALS 638,200 82,900 721,100 -1U8- Future Water Requirement s of the City of San Luis Obispo As will be discussed in detail in Chapter IV, the most pressing water resource problem presently facing San Luis Obispo County is considered to be the development of an additional water supply for the City of San Luis Obispo, Estimates of the City's future water requirements s prepared during the San Luis Obispo County Investigation^, formed a partial basis for various water supply plans considered,. Future water requirements were estimated by the application of pro- jected per capita water consumption rates to projected population increases. Historical population figures for the City were projected into the future by use of both the graphical comparison and the arithmetic progression methods 8 By use of the former method,, the slope of the projected population curve is influenced largely by the past experience of larger neighboring cities By use of the latter method^ the historical rate of population increase of the City being studied determines the slope of the population projection line for future years o Identical results were obtained from both of the foregoing methods. From an analysis of water consumption and population data available for most years since 1933 $ it was determined that the trend in daily per capita water consumption has remained fairly constant^ averaging 172„5 gallons per day Results of the foregoing studies indicate the future rate of popu- lation increase in the City will be about 690 per year,, and that the resulting increase in annual water use will be about 13U acre-feet per year,, Total demands on the City's water supply system resulting from the foregoing increases were estimated to be about ij.,,100 acre-feet in 1960 ? 5 5 UOO acre-feet -1U9- in 1970, and 6,700 acre-feet in 1980 o The indicated requirement of U,100 acre-feet in I960 would be nearly equal to the total amount of water presently available to the City, including 3^000 acre-feet from Salinas Reservoir,, Estimated rates of growth of population and water requirements for the City of San Luis Obispo are depicted on Plate 13, "Projection of Population and Water Requirement of City of San Luis Obispo 1*,, Monthly Demands for Water In the preliminary design of works to meet supplemental water re- quirements, consideration must be given to current practice in San Luis Obispo County as regards monthly distribution of seasonal water demand for irrigation and urban use. Demands for water for irrigation and urban purposes in San Luis Obispo County vary from month to month depending upon the type of land use and prevailing climatic conditions. Generally speaking, irrigation water is applied during the months from April through October for most crops. Multiple truck cropping practices in the Coastal and Santa Maria Units impose demands on irrigation water supplies throughout the year subject to the occurrence of precipitation. Irrigated hay and grain receive application of supplemental water during the winter months when deficiencies in precipitation occur . To achieve the desired soil moisture content for germination of seed, hay, grain, and bean lands are often preirrigated prior to planting. From analysis of measurements of application of water for irrigation purposes during the 1952-53 and 1953-5U seasons, it has been found that for certain crops, the monthly demand for water varies from zero to as high as 18.U per cent of the seasonal demand in Upper Salinas Unit. In the Coastal Unit, the extremes were found to be much less pronounced. Analyses of records of water consumption obtained from the Cities of Paso Robles and San Luis 150- Obispo reveal a more uniform monthly distribution than is the case with irrigation,, Estimates of average monthly distribution of seasonal demands for irrigation and urban x^ater are presented in Table 27° The estimates of monthly demands for irrigation water ? showed in Table 27j, for the Upper Salinas^, Cuyama,, Carrizo Plainj and San Joaquin Units are based upon applied water studies made in the Upper Salinas Unite Figures for the Coastal and Santa Maria Units are based on studies made in the Coastal Unito •151- TABLE 27 ESTIMATED AVERAGE MONTHLY DISTRIBUTION OF SEASONAL DEMAND FOR WATER IN SAN LUIS OBISPO COUNTY (In Per Cent of Season Total) • Upper Sal inagi, Cuyama^ Carrizo i Plain 5 and San Joaquin Units Coastal and Santa Maria Units Month • t Urban and o i Urban and Irrigation i suburban Irrigation : suburban October liio9 8o0 10,6 8.U November OoO 5.U 3.9 7,3 December 0,0 iio3 0,0 6,8 January- 0.0 U.3 0,0 6.7 February 0.0 Uol 0,0 5.7 March 0,0 5o0 0,0 6.3 April 8,5 7o0 7.5 7.3 May 10,7 io,5 lU.o 9,5 June 1U.2 12,0 15.9 9.8 July 17o8 li| 2 17.U 10.7 August 18,1 13o5 16,2 11.5 September 15»8 11,7 ljto5. 10.0 TOTALS 100.0 100,0 100.0 100.0 Supplemental Water Requirements Supplemental water requirements have been previously defined as the difference between the water requirements and the sum of safe ground water yield and safe surface water yield. In the case of a ground water basin, the safe yield cannot ordinarily be determined with any great accuracy until there are indications of an overdraft as previously defined. If an overdraft =152= does exists the present supplemental water requirement would be equal to the present overdraft <, Under ultimate conditions of development, the supplemental water requirement would be equal to the present overdraft plus the difference between present and ultimate water requirements The existence of a supplemental water requirement does not neces- sarily imply that further local water conservation development is infeasible«. On the contrary , a large portion if not all of the supplemental requirement may be met by additional local surface water developments Estimated present and probable ultimate requirements for supplemental water in San Luis Obispo County are discussed and evaluated in the following sections. Physical condi- tions in adjacent counties affecting supplemental water requirements in portions of San Luis Obispo County are also discussed^ Present Supplemental Water Requirements As shown previously,, presently available data indicate that none of the ground water basins in the Upper Salinas, Coastal , Cuyamac, Carrizo Plain,, and San Joaquin Units are overdrawn. The present mean seasonal water requirement of 68 ,,500 acre-feet in those units is apparently being satisfied by the safe yield of the developed water supply and supplemental water is, therefore ^ presently not required,, Throughout the County 5 irrigation development has been restricted to a large extent because of limited water supply development e In some local areas, temporary deficiencies have been reported,, These deficiencies have been primarily the result of poor well spacing or improper well construction and development as discussed in Chapter II<> These deficiencies are, there- fore, considered to be negligible and have not been included in present computations. -153- More extensive utilization of ground water supplies will eventually be manifested by overdraft conditions unless supplemental water is made avail- able. The continuance of a ground water level monitoring program would provide data required to ascertain the imminence of such overdraft conditionso The prevailing overdraft on ground water supplies in Santa Maria Valley is evidenced by perennial lowering of ground water levels, in all por- tions of the valley including the Santa Maria Unit. Evaluation of present supplemental water requirements for the Santa Maria Unit apart from the rest of Santa Maria Valley would be meaningless as the present supplemental requirement for water in the entire valley would have to be met in order to eliminate the overdraft in the Santa Maria Unit Accordingly , both present and probable ultimate supplemental water requirements have not been evaluated for that Unit. Probable Ultimate Supplemental Water Requirements For reasons discussed hereinbefore,, maximum safe ground water yield determinations have been made for only the Upper Salinas, Coastal, Carrizo Plain, and San Joaquin Units • The probable ultimate supplemental water requirement of the foregoing units is estimated to be approximately the 3>83 5 000 acre-feet as shown in following tabulations Acre-feet Ultimate water requirement 630^000 Presently developed water supply 1^7,000 Probable ultimate supplemental water requirement 583*000 Approximately 155,000 acre-feet, or 26 per cent of the probable ultimate supplemental water requirement of the four hydrologic units, can be -15U- met by further development of local water supplies, including about 29,000 acre- feet from increased ground water development, as discussed in Chapter II , and 126,000 acre-feet from surface water developments, as discussed in Chapter IV. The remaining 1*28,000 acre-feet of water would have to be imported from sources outside the County ^155- » CHAPTER IV. PLANS FOR WATER SUPPLY DEVELOPMENT The water supplies of San Luis Obispo County are generally adequate to meet present water requirements except for deficiencies presently existing in Santa Maria Valley and in other smaller areas wherein temporary local problems have arisen* With full development of the County's water resources, however, large quantities of water will have to be imported from sources outside the County Although attainment of ultimate conditions of development and water use will undoubtedly not occur until the distant future, the need for development of an additional source of water for the growing requirements of the City of San Luis Obispo is immediate In consideration of the ultimate water=using potential of the County and of the immediate problem facing the City of San Luis Obispo, it is desirable that a sound plan of water resource development be available for San Luis Obispo County at this time, and that it be prosecuted under a program of staged construction as the growth and attendant water needs of the County dictate o As a result of this investigation, such a plan has been developed which conforms to and is consistent with objectives of The California Water Plan In formulation of the plan for San Luis Obispo County, the following factors were considereds lo Provision for the water needs of the City of San Luis Obispo for the immediate futureo 2o Conservation of local waters now wasting to the ocean in order to provide to the maximum practicable extent for the anticipated future water needs of irrigated agriculture and urban and suburban lands throughout the County. =156= 3o Importation of water from sources outside San Luis Obispo County to satisfy the probable future water needs of the County in excess of new water yields of considered local water resource developments <> As was stated in Chapter I, the Division of Mater Resources for several years conducted state-wide surveys and studies for the State Water Resources Boardo These studies led to the formulation of The California Water Plan for full conservation,, control, and utilization of the State's water resources to meet present and future water needs for all beneficial purposes and uses in all parts of the State insofar as practicable* As stated previously, Bulletin No* 3 of the State Water Resources Board entitled "The California Water Plan", was published in May, 1957 • In addition to plans for development of the water resources of this investigation, plans are also presented therein to satisfy the ultimate water requirements of the County in excess of water made available by maximum practicable development of local water supplies* In general, major features of The California Water Plan are large multipurpose projects requiring relatively large capital expenditures. Plans presented in this report for the further development of local supplies would be such that the works could be integrated into the major features of The California Water Plane- Descriptions of plans considered for the conservation and utilization of local water supplies in San Luis Obispo County, and plans for importation of water from available sources outside the County,, are presented in this chapter under the sections designated; "Plans for Local Conservation Development", "alternative Plans for k'ater Supply Development", "Plans for Importation of Water", and "Flood Control" «, -157= „ Included herein are estimates of costs of the various plans, esti- mates of amounts of supplemental water that would be made available by their adoption and construction, and an economic comparison of the relative merits of the several plans Design of features of plans presented herein was necessarily of a r preliminary nature and primarily for cost estimating purposes „ More detailed investigation, which would be required in order to prepare construction plans and specifications, might result in designs differing in detail from those presented in this bulletin „ The resulting estimates of cost must also be considered of a preliminary nature and for the purpose of comparing the rela- tive merits of the considered projects „ Further consideration of a given project would require procurement of additional topography and other design data, as foundation drilling and materials analyses . Such work was beyond the scope of this investigation. The capital costs of dams, reservoirs, diversion works, conduits, pumping plants and appurtenances for water conservation and conveyance systems studied were estimated from preliminary designs based largely on data from surveys made during the current investigation, both by the Division of Water Resources and other cooperating agencies » Estimates of construction quantities were made from these preliminary designs . Unit prices of construction items were determined from recent contract bid cost data for projects similar to those under consideration or from manufacturers list prices and are considered representative of prices prevailing in 195^° Estimates of capital cost includ- ed costs of rights of way and construction, 10 per cent of construction costs for engineering, 15 per cent of the construction costs for contingencies, and interest during construction computed at the rate of four per cent per annum for one°half the construction period. Estimates of annual costs included >158< interest on the capital investment at 3°5 per cent per annum, amortization over a I^O-year period on a }<,$ per cent sinking fund basis, replacement costs, operation and maintenance costs, and cost of electrical energy required for pumpingo Replacement costs were estimated as the annual costs of accumulation of a sinking fund, bearing three and one-half per cent interest, equal to the estimated costs of those items of dam construction such as gates, valves, and other metal work, and pipe line and pumping plant equipment which, it is estimated, would require replacement during the assumed repayment periodo Operation and maintenance costs were estimated for dams and reservoirs on the basis of the costs shown in the following tabulations $0o20 per acre-foot for first 25,000 acre-feet of storage capacity $0ol0 per acre-foot for next 75?000 acre-feet of storage capacity $0o06 per acre-foot for next 90Q 5 000 acre-feet of storage capacity Plans for Local Conservation Devel opment The erratic occurrence of runoff in San Luis Obispo County severely limits the extent to which local water supplies can be utilized without regu- latory storage capacity to equalize stream flow from winter to summer months and from wet periods to ensuing periods of drought At the present time, this required regulatory storage capacity has largely been developed in the under- ground storage basins > Studies by the Division of Water Resources indicate that a maximum of approximately 200,000 acre-feet of water per season presently wasting to the ocean can be economically conserved for beneficial use in San Luis Obispo County through further regulation by surface and underground reservoirso The two primary methods by which a portion of the presently wasted water might be captured, including increased development of ground water supplies and storage of nunoff in surface reservoirs, are discussed in the -159- following paragraphs o As at present, it is anticipated that direct diversions of surface runoff will continue to comprise a minor portion of the total developed water supply* Further Development of Ground Water Storage It is estimated that in excess of 200,000 acre-feet of underground storage capacity has been utilized to date in the County, most of which has been in the Paso Robles Basin, of the Upper Salinas Unit,, Future growth and economic development in the County will necessarily be reflected in further utilization of the underground reservoirs Correspondingly, ground water levels will be further lowered during drought periods, thus providing storage space for percolation of stream flow and precipitation during subsequent wet periods,. As set forth in Chapter II, it is estimated that ground water basins in San Luis Obispo County, with increased utilization as will occur by the additional development of overlying lands, could provide an additional yield of about 33 3 000 acre-feet per season,, To attain this increased yield it would be necessary to dewater in excess of U00,000 acre-feet of additional ground water storage capacity,. Such additional utilization would not, however, result in the creation of excessive pumping lifts nor would withdrawals from the basins under such conditions exceed average annual recharge thereto. The Paso Robles and Arroyo Grande Basins are the most important in the County with respect to possibilities for increased ground water development. Planned operation of ground water basins would result in increased yield not only through salvage of a portion of the runoff presently wasting elimination of to the ocean 5 but also, in certain areas, through reduction or nonbeneficial consumptive use of water by phreatophyteso It is estimated -160- „ = that up to 12 5 000 acre°feet of water per season may be conserved by elimina- tion of phreatophytic growth in ground water basins of San Luis Obispo County For purposes of review^ there is presented in Table 28 a summary of estimated present and anticipated maximum practicable safe seasonal yield of ground water supplies in San Luis Obispo County exclusive of the Santa Maria and Cuyama Units. TABLE 28 ESTIMATED PRESENTLY DEVELOPED AND MAXIMUM PRACTICABLE SAFE YIELD OF GROUND WATER SUPPLIES IN PORTIONS OF SAN LUIS OBISPO COUNTY AND VICINITY In Acre°Feet s Estimated safe seasonal yield Hydrologic unit gPresently developed;; Maximum UPPER SALINAS UNIT 26,900 Zi5,oooa COASTAL UNIT 13,800 21*, 800 CARRIZO PLAIN UNIT 600 600 SAN JOAQUIN UNIT TOTALS la, 300 70,1*00 a Q Includes yield of Paso Robles Basin within Monterey County As set forth in Chapter II, the maximum safe seasonal yields of certain ground water basins were limited for the purposes of this bulletin to the estimated mean seasonal water requirements of overlying lands not affected by proposed surface water supply developments. Therefore, these estimated mean seasonal water requirements of overlying lands were deducted from estimated gross yields of proposed reservoirs to obtain net safe seasonal yields thereof =161= r . Potential Surface Storage Developments Investigation of potential surface storage development's in San Luis Obispo County included studies to determine the amounts of supplemental water that could 'be developed by constructing reservoirs of various storage capacities at the sites considered, geologic investigations to determine suit- ability of dam sites in regard to types and heights of dams,, and estimates of capital and annual costs for purposes of establishing economic relationships between the various storage capacities considered at the several sites Preliminary reconnaissance was made of 58 potential dam and reservoir sites in San Luis Obispo County and vicinity, after which efforts were concen- trated on more detailed investigation of 17 of the sites considered more favorable for development o The sites given reconnaissance examination and subsequently eliminated on the basis of poor geologic conditions, limited water supply, high capital costs, or excessive unit costs of water are listed in the following tabulation and shown on Plate 14s Dam and reservoir Stream Dam and reservoi Stream Upper Salinas Unit American Canyon Salinas River Middle Mountain Cholame Creek Pozo Salinas River Upper Cholame Cholame Creek Salinas No 2 Salinas River Lower Cholame Cholame Creek Salinas No. 1 Salinas River White Canyon White Canyon Upper Atascadero Atascadero Creek Creek Rocky Gorge Graves Creek Palo Prieto Canyon Palo Prieto Upper Jack Jack Creek Canyon Creek Middle Jack Jack Creek La Panza San Juan Creek Upper Paso Robles Paso Robles Creek Shedd Canyon Shedd Canyon Lower Paso Robles Paso Robles Creek Creek Mustang Tributary to Huerhuero Huerhuero Creek Cholame Creek Carrizo Plain Unit Elkhorn Unnamed tributary to Carrizo Plain -162- z „ Dam and reservoir Stream Dam and reservoir Stream Coastal Unit Upper Burnett Burnett Creek Dark Range Toro Creek Lower Burnett Burnett Creek Estero Toro Creek Lone Tree Arroyo de la Cruz Cerro Alto Morro Creek Chileno Arroyo de la Cruz Los Osos Los Osos Creek Crows Nest Steiner Creek Laguna Lake San Luis Obispo Red Mountain San Simeon Creek Creek Cypress Mountain Santa Rosa Creek See Canyon See Canyon Creek Mammoth Rock Santa Rosa Creek Pismo Pismo Creek San Geronimo Villa Creek Stone Cabin Lopez Creek Cayucos Cayucos Creek Lopez Noo 2 Lopez Creek Rusty Peak Old Creek Basque Basquez Creek San Luisito San Luisito Creek* San Bernardo San Bernardo Creek* * Not shown on Plate 14? see description below Reconnaissance investigation of potential dam and reservoir sites in the Carrizo Plain and San Joaquin Units^ as well as eastern portions of the Upper Salinas Unit 5 together with hydrologic studies^ indicated that there are few feasible sites 5 and that present waste of water from those areas is either nonexistent or insignificant in comparison with present and probable future supplemental water requirements o Some sites in the foregoing tabulation,, however,, were studied for possible development as regulating reservoirs for imported supplies* A number of sites suitable for smaller development , such as San Geronimo, Cayucos^ Estero, Cerro Alto,, and Rocky Gorge, also San Luisito and San Bernardo, which are located on minor tributaries of Chorro Creek east of Morro Bay, were reconnoitered and found to have possibilities for providing water supplies for smaller communities «, Because of their limited storage capacity or yield s further study of these sites was considered beyond the scope of this investigation, Subsequent investigations., however,, may prove these sites to be highly desirable for construction by individual farmers or by some of the smaller communities. *163= Preliminary designs and cost estimates were made for the remaining 17 dams and reservoirs investigated. In most cases, estimates of cost and of reservoir yield were made for several capacities at each site. All sites exa.mi.ned are shown on Plate Ik, entitled "Existing and Potential Water Supply Developments". Those sites at which preliminary designs and cost estimates were prepared are listed in the following tabulation: Dam and reservoir Stream Dam and reservoir Stream Upper Salinas Unit Rinconada Salinas River Lower Jack Jack Creek Cantera Salinas River Santa Rita Santa Rita Creek Lower Atascadero Atascadero Creek San Miguelito Nacimiento River Dover Dover Creek Jarrett Shut -In Nacimiento River Coastal Unit Bald Top San Carpoforo Creek Santa Rosa Santa Rosa Creek Ragged Point San Carpoforo Creek Whale Rock Old Creek Yellow Hill Arroyo de la Cruz Wittenberg Arroyo Grande Palmer Flats San Simeon Creek Creek San Simeon San Simeon Creek Lopez Arroyo Grande Creek It will be noted in the foregoing tabulation and on Plate Ik that a number of alternative sites were considered for the construction of dams on several of the streams in the County „ Final decision as to the site or sites considered most feasible of development on a particular stream or stream system was reached after consideration of the various engineering and economic factors involved. In some cases } the limited water supply precluded more than a single development on a given stream. In other instances, sites were eliminated from further consideration due to apparent limitations as to geologic conditions or after preliminary design and cost estimates revealed excessive capital or unit costs of water. -l6h- ° Prior to completion of this bulletin , the Monterey County Flood Control and Water Conservation District initiated and essentially completed construction of Nacimiento Dam and Reservoir,, Further study of the El Nacimiento,, Winchester Ranch, and Pebblestone Shut=In on the Nacimiento River as possible sites for the development of supplemental water supplies for San Luis Obispo County would serve no practical purpose , and they were there- fore eliminated from further consideration in this bulletin, Although several alternative storage capacities were investigated at the final chosen sites, detailed discussions of the proposed developments are presented following for only one capacity at each site,, Detailed cost estimates for all structures considered are presented in Appendix L of this bulletino Estimates of monthly runoff throughout the base period were made for each of the chosen sites , using the previously described method developed by Troxell wherein consideration is given to available runoff records for the area as well as precipitation^, slope s vegetative cover, and absorptive char- acter of the respective watersheds „ Monthly distribution of estimated seasonal runoff was estimated by correlation with long<=term records for nearby streams At the Lower Jack and Yellow Hill sites, actual records of measured runoff were available for a portion of the base period* The resulting recorded or estimated monthly runoff occurring during the base period at Salinas and Nacimiento Dams 5 in addition to the 11 sites chosen for study, is presented in Appendix J Annual summaries of the runoff values at proposed dam sites are presented in Table 29 =165< I 88888 800000000 OOOOOO O O Q Q Er\ 'r\ en jj- jf r-vt-vja- oven f\\0 «-l O O O k Ok ^. Ok Ck Ot Ot <( ^ A <^jj- O vo en ONVO VO *^ ON 8 0000Q O O o0000q o o OOOOO Oo o O UNjJ- fv. UN UN O J* C\ O st VO «AjJ- t-v J" en Ok Ok Ck Ok os Ok Ck o. c\ o. Ok «\ Ok Ok Ok P JLT CO »-) CM vo NtOOHH fvCnCM UN UN fv o o o o o OOOOO 00000 o o o o o §0000 OOOOO »JtO CO J- ONVO o o t~--!i-t VO CM J- Ok Ok Ok Ck Ck Ok Ck Ok Ok o\ on cm co en UN H ITiFMOtN 3 cnCM. o-» r-t «H 00000OOOOO OOOOO OOOOO00000 o oO CO o 00000 OOOOO00000 OOOOO o o j- ON C\ o ON CM UNVO VO UN.-I O st CO co CO Ok Ck Ck. Ok Ok Ok Ok Ok Ok Ok Ok Ok Qk Ok Ok Cn r-l ONVO VO COVQ St UNVO UN CM ONJ- v— j3- uno vo cm uNvo en en N H CM CM c fa ® O O O O O O OOOOO O O O O O O OVOP\ UNCO O co UNCO H H un en U> o-t (X -O Ck Ok ok ok Ok ft Ok 0. Ok Ok Ok t Ok Ok Ok Ok UN e-1 t*~vo P"fl st ono en cm ONcH CO VO w enst t>. UN ONJ- un en en CM .•-< CnJ CM CM en 4 E-i a o OOOOO 00000OOOOO OOOOO o OO UNCO C\t^ fv.Cn CM UNfv. CO j± coOjf o T3 Oj o» Ok 0% Ok Ok Ok Ok Ok Ok Ok Ok Ok Ck Ok H UNjJ- UN UN UN Hvojf H O HMrt CM J- 00 O o 00000OOOOO OOOOO000 OOOOO o o 15 "f VO t"v UNVO CO vovo fv. un en rt OO H H N Cv, CM Ck o, «k o» 04 Ok Ok Ok Ok Ok Ck. Ok Ok Ok Ok st t>st vp t> fv.uN envo on r-vao es! uno u\ih en fv. t-v UN CM CM UN UN CMrH «H 00000OOOOO OOOOO00000 OOOOO o VO UN VO t-vCO ON O «-l cm en J- un 1 .t^co ON O en en en cn-d- ST jlJ- jH- Jt St ststsi- UN UN O UN( o S en St UN W ON * ON ON > 6-3 t-l =166= Monthly net evaporation rates throughout the base period were estimated for each reservoir, based primarily upon records of evaporation at Salinas Reservoir adjusted for differences in precipitation and temperature occurring at each of the individual reservoirs „ Values of net evaporation were computed as the difference between gross evaporation and the consumptive use of water by native vegetation in the reservoir area. The resulting average values of estimated monthly unit net evaporation at the various reservoir sites are presented in Table 30. =167= N MOOnOnCOi-Ic^nOC— iaoooo o CD WO OOHOH m_3U\_^_^ ft O oo oooooooooo CM a i i i o o OnCM _3" cr\ CNNO CvlrlO r— IAnO vO cd WHOOOOW _3"UMr\ir\_3 ON CD oo oooooooooo CM rH I 1 II CO Xi cd to o OsvO _^ On cm Cvj j- O\0O iH O f^ « HO HOHOh^ c^_a--=r CA CO cd oo oooooooooo G I I I I a) CO a o CD OlAOs^-HO CMOcOCJOf^ CA 1A CO Oooooooooooo* • * • • © • © O O t> • -P c 1)10 ft o Q0) CO +3 W O c •H m P h O HosH^OO f^COOCOHO <*\ 0) CD PL, T3 ^owhwhh r*\,cN._=r_=Tm UN ft C ftT3 CO oooooooooooo C3 0) 1 y II c bO M bD CO *« ©• •* po p •H -P 4» HOC •H f^CO CO ON MO -^ CM iH cnu\rHNO| CM C Jh II f^O CM rH C°\ H CM \AvO r- C— XA CO S3 W) cO P oo»oooo©«eo *j •H *-3 g oooooooooooo! CM co SI •£ 10 10 cO a c r •H CO CO rH co a) CO cO ^4o P U 03 cu H\AI>- r— O c^OnpH cni-rNHMOl -3- c^Oo^CMXACM H 1AMO C— C-~XA| CA ft ^ e co P CD CO P oooooooooooo! CM £ c 110 O CO t-3 CO M u «3J CD X! , U U ^ ^> U -168- , Sedimentation in proposed reservoirs was estimated from records of sediment accumulation at existing reservoirs in central and southern California, including those available for Salinas Reservoir* Use was also made of the basic sedimentation equation presented in the report entitled "Flood Frequencies and Sedimentation from Forest Watersheds 8 ', by Henry W. Anderson, U. S. Forest Service, dated August, 19h9° Reservoir operation studies were based on the effective storage capacity that would remain after 20 years of sedimentation, which period represents one-half of the amortiza~ tion period assumed for dam and reservoir costs. The constructed capacity of the reservoirs is hereinafter referred to as the "gross reservoir storage capacity", and the effective capacity remaining after 20 years of operation as the "net reservoir storage capacity" o Values of sedimentation utilized for the various reservoirs are shown in the following tabulations Sedimentation allowance Reservoir in acre-feet Upper Salinas Unit Lower Jack 500 Santa Rita 500 San Miguelito 1 5 000 Jarrett Shut-in 2,000 Coastal Unit Bald Top 500 Ragged Point 500 Yellow Hill 1,000 San Simeon 500 Santa Rosa 500 Whale Rock 500 Lopez 1,000 It is possible that more conservation storage in the foregoing reservoirs could be preserved by keeping burned areas to a minimum and maintaining good vegetative cover in the tributary watersheds. •169= Yields of new water for various assumed capacities at each of the sites receiving detailed consideration were determined from monthly operation studies conducted over the chosen base period, 1935-36 through 1950-51. Reservoirs were first operated on a "gross" safe yield basis in which it was assumed that all runoff at each dam site was susceptible of regulation by the reservoir. Gross yields thus obtained were then reduced to net yields, assumed to be equal to the estimated amounts of water available for storage and utilization which would not otherwise be put to beneficial use downstream under anticipated ultimate conditions of development by increased utilization of the ground water basins e Therefore.* proposed reservoirs were not credited with presently undeveloped ground water yield which could ultimately be put to beneficial use on lands overlying ground water basins. Estimated maximum safe ground water yields for each of the ground water basins identified during this investigation were presented previously in Table 12. The monthly distribution of yields from reservoirs in the Upper Salinas Unit was based upon an irrigation demand schedule. For the Coastal Unit, the monthly distribution of demand was assumed to reflect a 75 per cent irrigation demand schedule and 2$ per cent urban demand schedule. Following is a tabulation showing monthly demand schedules used for reservoir operation studies in the two foregoing units. -170- « Monthly demand in per cent of annual total Month Upper Salinas Unit Coastal Unit October 114.9 10„0 November OoO hoi December OeO 1.7 January OeO 1.7 February OoO loll March OoO lo6 April 8,5 7.1* May 10o7 12o9 June llu2 iluU July 17c8 15 08 August 18 .1 I5o0 September 15.8 13.1* TOTALS 100,0 100*0 Spillways for proposed dams in San Luis Obispo County were designed to pass the probable peak discharge from a flood having an estimated frequency of once in one thousand years occurring at a time when the reservoir would be full. Consideration was given to the effect of surcharge reservoir storage on reducing peak discharges over spillways at all reservoirs except Lower Jack and Santa Ritao Effective reductions in estimated peak flows were estimated to vary from 7 to 65 per cent, based on routing studies • For the Lower Jack and Santa Rita Reservoirs , the effect of surcharge storage was found to be negligible , and no reduction in peak flow was considered for spillway design purposes o In all cases 3 spillway designs are considered to be conservativec The valuations of lands and improvements required for the construction of proposed dams and reservoirs were based upon data obtained from the San Luis Obispo and Monterey County Assessors « Estimates of the costs of necessary highway relocations were furnished by the Monterey County Flood Control and Water Conservation District, the San Luis Obispo County Road Commissioner and the State Division of Highways =171= Presented following are brief discussions of the 11 dam and reservoir sites considered most favorable of development in San Luis Obispo County and vicinitye The results of investigation of these sites are depicted graphically on Plate 21, entitled "Relationship Between Storage Capacity of Reservoirs and Capital Costs" $ Plate 22, entitled "Relationship Between Storage Capacity of Reservoirs and Net Safe Seasonal Yield"! and Plate 23, entitled "Relation- ship Between Net Safe Seasonal Yield of Reservoirs and Annual Unit Cost" Lower Jack Dam and Reservoir The Lower Jack dam site is located on the lower reach of Jack Creek in the Paso de Robles land grant, about six miles west of the twon of Templeton» The site has been variously called Lower Jacreek and Lower Jack Creek in the paste Consideration was given to con«= struction of a dam and reservoir at the Lower Jack site for storage of surplus waters of Jack Creek, and utilization of the waters so conserved in the Upper Salinas Unite The Lower Jack dam site was mapped at a scale of one inch equals 100 feet, with a contour interval of five feet, and the reservoir area was mapped at a scale of one inch equals 1*00 feet, with a contour interval of 10 feet, by the U. S. Bureau of Reclamation in 19h6<> Reservoir areas and storage capacities, computed from the reservoir area map, are presented in Table 31. -172- TABLE 31 AREAS AND CAPACITIES OF LOWER JACK RESERVOIR Depth i Water surface s Water s Storage of water : t elevation^ i surface 5 capacity, at dam, i : UoSoGoSo datura, s area, s in in feet i ; in feet : in acres : acre-feet 990 10 1,000 k 10 20 1,010 18 120 30 1,020 39 1*10 ko 1,030 60 900 50 1,01*0 98 1,700 60 1,050 130 2,81*0 70 1,060 160 U,290 80 1,070 190 6,01*0 90 1,080 220 8,090 100 1,090 260 10,500 110 1,100 310 13,300 115 1,105 330 15,000 120 1,110 350 16,600 130 1,120 1*10 20,1*00 11*0 1,130 1*70 25,000 150 1,11*0 560 30,000 160 1,150 660 36,100 170 1,160 750 1*3,100 180 1,170 850 51,100 =173= , Based upon preliminary geologic reconnaissance, the Lower Jack dam site is considered suitable for either an earthfill or masonry type of dam. Geology of the site was investigated by the U,, S„ Bureau of Reclamation in 19U7, and by the Division of Water Resources in 1953° No exploratory drilling or trenching of the foundation has been done at this site, nor of the borrow areas Bedrock at the dam site consists of massive, fairly well -bedded, Cretaceous sandstones, and some conglomerates,, The beds strike nearly east- west across the southeast trending channel, and have a I4O to 50 degree dip downstream* About 200 feet upstream from the axis, a fault crosses the channel, bringing shales of the reservoir area in contact with the sandstones at the dam site The sandstones are fractured and would probably require moderate grouting. There is considerable soil creep on the right abutment, and possi- bly some small slides In the channel section of the dam, it is estimated that a depth of two feet of gravel would have to be stripped, and the bedrock shaped under the impervious core. It is further estimated that about six feet of surface soil and six feet of weathered rock would have to be removed from the left and right abutments for the impervious section. Yield studies were made for reservoir storage capacities of 15,000 and 25,000 acre-feet at the Lower Jack site and are summarized in Appendix K The estimates of safe seasonal yield obtained from these studies are as follows % Gross Height reservoir Safe seasonal of storage yield, in dam, capacity, acre-feet in feet in acre-feet Gross : Net 135 15,000 5,600 3,U00 160 25,000 6,800 1|,600 »17li- Differences between gross and net yields presented in the foregoing tabulation represent releases required to maintain water levels in downstream ground water basins at elevations which would prevail without operation of the reservoir under present conditions of developmento The relationship be- tween reservoir storage capacity and net safe seasonal yield for Lower Jack reservoir is shown graphically on Plate 22 After consideration of results of the yield studies., geologic reconnaissance^ and topography of the site 5 detailed estimates of cost were prepared for an earthfill dam and reservoir of both the foregoing sizes,, which estimates are presented in Appendix L„ General features of both sizes of dam and reservoir are listed in Table 32 =175= TABLE 32 GENERAL FEATURES OF TWO SIZES OF DAM AND RESERVOIR AT THE LOWER JACK SITE ON JACK CREEK Characteristics of Site Drainage area— 25 • 3 square miles Estimated average seasonal runoff --11,100 acre-feet Estimated average net seasonal depth of evaporation--2.3li feet Estimated sedimentation—500 acre-feet Elevation of stream bed, U.S.GoS. datum— 990 feet sGross reservoir storage capacity, : in acre-feet 15,000 25,000 Earthfill Dam Crest elevation, in feet, U.SoG.So datum 1A25 1A50 Crest length, in feet 550 670 Crest width, in feet 25 25 Height, spillway lip above stream bed, in feet 115 11*0 Side slopes, upstream and downstream 2o5sl 2.5:1 Freeboard, above spillway lip, in feet 20 20 Volume of fill, in cubic yards 61*2,000 1,001,000 Reservoir Surface area at spillway lip, in acres 330 h70 Net storage capacity at spillway lip, in acre-feet lii, 500 2l*,5oo Type of spillway Ogee weir with concrete chute Spillway discharge capacity, in second feet 25,000 25,000 Type of outlet 36-inch l*2-inch diameter diameter steel pipe steel pipe Estimated net safe seasonal yield, in acre-feet 3,i|00 U,600 Capital Cost Dam and reservoir .,30^,000 $1,751,000 Per acre-foot of storage 87 70 Per acre-foot of net safe yield 38U 381 Annual Cost Dam and reservoir 66,000 87,000 Per acre-foot of net safe yield 19.1*0 18,90 Per acre-foot of incremental net safe yield 17c50 176= For each height of dam the earthfill structure would comprise an impervious core of select earth material,, and upstream and downstream sections of pervious free-draining material. The upstream face of the dam would be protected against wave action by rock riprap placed to a depth of three feet normal to the slope Earthfill material considered suitable for the imper- vious section of the dam occurs within two miles upstream of the site It is estimated that abundant pervious material could be obtained from the reservoir area and from surrounding slopes o Sandstones within the immediate area could probably be quarried for riprap. The spillway for either height of dam would have a discharge capacity of 25>c,000 second^feeto It was designed as a concrete-lined overpour chute 5 located on the right abutment,, with an ogee weir control section,, The chute would discharge into a small ravine downstream from the toe of the dam The outlet works for either height of dam would have a concrete inlet structure at the upstream toe near the right abutment^ with a steel trash rack structure at the entrance A concrete pressure conduit beneath the dam, founded on bedrock^, would extend from the inlet tower to the valve chamber located at the axis of the dam A reinforced-concrete pipe would ex= tend from the valve chamber to the control valve house s and would house an access passageway to the valve chamber as well as a steel outlet pipe sup- ported on cradles o Downstream releases would be controlled by valves located within the control house It was estimated that either height of dam could be constructed within one year^ and that summer flow of Jack Creek could be diverted through the outlet conduit For illustrative purposes., a plan 3 profile,, and section of a dam creating a reservoir with storage capacity of 25^000 acre-feet at the Lower Jack site are shown on Plate 16« =177= . Santa Rita Dam and Reservoir . The Santa Rita dam site is located on Santa Rita Creek about three miles upstream from its confluence with Paso Robles Creek in the Asuncion Land Grant. Consideration was given to con- struction of a dam and reservoir at the Santa Rita site for storage of flood- waters in Santa Rita Creek and utilization of water so conserved in the Upper Salinas Unit* The Santa Rita dam site was mapped at a scale of one inch to 50 feet s with a contour interval of five feet, by the U„ S„ Bureau of Reclamation in 1946 c Reservoir areas and storage capacities for various stages of water surface elevation were computed from U<> S„ Geological Survey quadrangles at a scale of ls24,000, with a contour interval of 20 feet, and are shown in Table 33 •178- TABLE 33 AREAS AND CAPACITIES OF SANTA RITA RESERVOIR Depth ! Water surface : Water : Storage of water ; \ elevation , % surface : capacity, at dam, < \ UoSoGoSo datum, : area, : in in feet : in feet i in acres s acre »feet 1,005 5 1,010 1 2 15 1,020 1* 30 25 1,030 10 100 35 1,01*0 19 21*0 k5 1,050 3h 510 SS 1,060 51 930 65 1,070 66 1,520 75 1,080 82 2,260 85 1,090 120 3,270 95 1,100 150 1*,620 105 1,110 190 6,320 115 1,120 220 8,370 121, 1,129 260 10,500 125 1,130 270 10,800 135 1,11*0 320 13,800 138 1,11*3 3U0 1U,800 11*5 1,150 390 17,300 155 1,160 1*60 a, 600 =179= » A spillway saddle is located on the ridge northeast of the left abutment* The geology of the site was investigated by the U. S, Bureau of Reclamation in 19U7 and by the Division of Water Resources in 1953 • No exploratory drilling or trenching of the foundation has been done at this site, nor of the borrow areas „ Based upon preliminary geologic reconnaissance, the Santa Rita dam site is considered suitable for an earthfill danu Bedrock at the dam site consists of sandstone, siltstone, and shale of Cretaceous age Outcrops are found only in deep gullies and in roadcuts* All exposures exhibit fairly tight fractures and joints, and light to moderate grouting would be required . The rocks strike directly across the stream bed at the axis and dip 1*0 to 50 degrees upstream. About 100 yards downstream the beds dip downstream, suggesting the presence of major geologic structure in the area« It is estimated that an average depth of 16 feet of sand, gravel, and weathered rock would have to be stripped in the channel section under the impervious section of the dam. An estimated six feet of soil and eight feet of weathered rock would have to be stripped from both abutments for the impervious sectiono Stripping depths to sound rock for the spillway would be the same as on the abutments Yield studies were made for reservoir storage capacities of 10 s 000 and 15,000 acre~feet at the Santa Rita site, results of which are summarized in Appendix K„ The estimates of safe seasonal yield obtained from these studies are as follows; »180= , Gross Height reservoir Safe seasonal of storage yield in dam capacity acre-feet in feet in acre-feet Gross : Net 12U 10,000 U,5oo 2,700 138 15 5 000 5,200 3,200 Differences between gross and net yields presented in the foregoing tabulation represent releases required to maintain water levels in downstream ground water basins at elevations which would prevail without operation of the reservoir under present conditions of development * The relationship between reservoir storage capacity and net safe seasonal yield for Santa Rita Reservoir is shown graphically on Plate 22 After consideration of results of the yield studies, geologic recon- naissance, and topography of the site, detailed estimates of cost were prepared for an earthfill dam and reservoir of both the foregoing sizes, which estimates are presented in Appendix L General features of both sizes of dam and reservoir are listed in Table 3ii» =181- — TABLE 3ii GENERAL FEATURES OF TWO SIZES OF DAM AND RESERVOIR AT THE SANTA RITA SITE ON SANTA RITA CREEK Characteristics of Site Drainage area—=18 .6 square miles Estimated average seasonal runoff°-9,800 acre-feet per year Estimated average net seasonal depth of evaporation 2.3k feet Estimated sedimentation~-500 acre-feet Elevation of stream bed, U.S.G.S. Datum—1,005 feet Gross reservoir storage capacity, in acre-feet 10,000 15,000 Earthfill Dam Crest elevation, in feet, U.S.G.S. datum l 9 lhh 1,158 Crest length, in feet hhl 520 Crest width, in feet 25 25 Height, spillway lip above stream bed, in feet 12h 138 Side slopes, upstream and downstream 2.25:1 2.5:1 Freeboard, above spillway lip, in feet 15 15 Volume of fill, in cubic yards 1*22,600 666,1*30 Reservoir Surface area at spillway lip, in acres 261* 310. Net storage capacity at spillway lip, in acre-feet 9,500 il*,5oo Type of spillway Ogee weir with concrete chute Spillway discharge capacity, in second feet 20,000 20,000 Type of outlet Pipe encased Pipe encased in concrete in concrete Estimated net safe seasonal yield, in acre-feet 2,700 3,200 Capital Costs Dam and reservoir $1,107,000 $1,1*01*, 000 Per acre=foot of storage 111 Per acre-foot of net safe yield lllO 1*39 Annual Costs Dam and reservoir $56,800 $70,700 Per acre-foot of net safe yield 21.00 22.10 Per acre-foot of incremental net safe yield 27.80 »182» o For each height of dam,, the earthfill structure would comprise an impervious core of select earth material^, and upstream and downstream sections of free-draining material,, The upstream face of the dam would be protected against wave action by rock riprap placed to a depth of three feet normal to the slope o It is estimated that sufficient material, both pervious and impervious , and riprap , could be obtained within one and one -half miles of the dam site in the reservoir area The spillway for either height of dam would cut through the saddle northeast of the left abutment discharging into a ravine downstream from the toe of the dam, and would have a discharge capacity of 20,000 second-feet The spillway would be designed as a concrete-lined overpour chute with an ogee weir control section,, The outlet works for either height of dam would consist of a 36-inch diameter steel pipe encased in concrete., placed in a trench excavated to sound rock beneath the dam» Releases from the reservoir would be controlled at the upstream end of the outlet by means of hydraulically operated slide gates in an inclined intake structure on the slope of the right abutment upstream from the dam„ Releases would be further regulated by a Howell-Bunger valve at the downstream end of the outlet,, It was estimated that either height of dam could be constructed within one year and that summer flow of Santa Rita Creek could be diverted through the outlet conduit* For illustrative purposes , a plan, profile, and section of a dam, creating a reservoir with a storage capacity of 15,000 acre-feet at the Santa Rita site, are shown on Plate 17 =183= San Miguelito Dam and Reservoir a The San Miguelito dam site is located in Monterey County on the upper reaches of the Nacimiento River, about two miles upstream from the mouth of Gabilan Creek and about nine miles up- stream from Jarrett Shut-in dam site. The reservoir area lies within Hunter- Liggett Military Reservation. Consideration was given to the construction of a dam and reservoir at the San Miguelito site for storage of floodwaters of Nacimiento River and utilization of water so conserved in the Upper Salinas Unit. The San Miguelito dam site and two saddle dam sites were mapped at a scale of one inch equals 100 feet, with contour intervals of ten feet, by the Division of Water Resources in 195Uo Reservoir areas and storage capacities for various stages of water surface elevation were computed from U S. Geological Survey quadrangles at a scale of 1:2U,000, with contour intervals of 20 feet, and are shown in Table 35. -1814- TABLE 35 AREAS AND CAPACITIES OF SAN MIGUELITO RESERVOIR Depth i Water surface : Water ; Storage of water : t elevation , \ surface s capacity, at dam 5 : : UoS.G.S. datum, % area, ; in in feet ! i in feet 3 in acres % acre-feet i,no 10 1,120 2 6 20 1A30 6 50 30 i,il*o 13 11*0 ko 1,150 30 360 50 1,160 55 780 60 1,170 90 1,510 70 1,180 180 2,860 80 1,190 3U0 5,U60 90 1,200 5ii0 9,860 100 1,210 820 16,700 110 1,220 1,150 26,500 120 1,230 1,570 1*0,100 126 1,236 1,800 50,200 130 l,2ii0 1,980 57,900 11*0 1,250 2,1*00 79,800 150 1,260 2,800 106,000 158 1,268 3,060 129,1*00 160 1,270 3,120 136,000 170 1,280 3,1+1*0 168,000 180 1,290 3,770 20)4,000 190 1,300 li,210 2liU,000 >185< Basec| on preliminary geologic reconnaissance, the San Miguelito dam site is considered suitable for an earthfill danio Geology of the site was investigated by the Division of Water Resources in 1953* No exploratory drilling or trenching of the foundation has been done at this site, nor of the borrow area* Bedrock at the site is a mixture of conglomerates and sandstones of Cretaceous age Outcrops are thickly bedded and prominently jointed. Talus is piled up 50 to 70 feet at the base of the abutments. Moderate to heavy grouting would be required., Stripping estimates are apt to be in error due to the presence of large boulders which conceal the extent of deposits , For cost estimating purposes, it was estimated that an average depth of about 20 feet of gravel, boulders, and bedrock would have to be stripped from the channel section. It was further estimated that stripping of about 15 feet of talus rubble and boulders and five feet of bedrock for shaping would be required on the right abutment and up to .30 feet of stripping would be required on the left abutment . About 80 per cent of the stripped material could probably be salvaged for use as riprap and in the pervious section of the dam. Based on a preliminary reconnaissance, it is believed that adequate materials for the impervious core could be obtained from within the reservoir area., Yield studies were made for reservoir storage capacities of 50*000 acre-feet and 130 5 000 acre-feet at the San Miguelito site. The estimates of safe seasonal yield obtained from these studies with San Miguelito Reservoir operated as a secondary development coordinately with existing Nacimiento Reservoir were as follows? •186- j Gross reservoir Safe seasonal storage yields capacity in acre-feet in acre-feet Gross s Net 126 50,000 7,700 6,000 158 130 5 000 17*000 13,000 Since flows of the Nacimiento River along with flows of the Salinas River have historically been partially utilized in the upper and lower Salinas River basins both by direct diversion and through recharge of ground water basins therein , and since the Monterey County Flood Control and Water Conservation District is constructing a dam and reservoir at the Winchester Ranch (Nacimiento) site downstream., water yields of San Miguelito Reservoir shown in the foregoing tabulation are based on storage of only the flows of Nacimiento River which would waste to the ocean under present conditions of water use in the Salinas River Basin and with Nacimiento Reservoir operated to obtain its maximum yield,. Difference between gross and net yields presented in the foregoing tabulation represent releases required to maintain water levels in the downstream ground water basins at elevations which would prevail without reservoir operation The relationship between reservoir storage capacity and net safe seasonal yield for San Miguelito Reservoir is shown graphically on Plate 22 <, After consideration of the results of the yield studies , geologic reconnaissance!, and topography of the site, detailed estimates of cost were prepared for earthfill dams and reservoirs for each of the foregoing sizes s which estimates are presented in Appendix L General features of both sizes of dam and reservoir are listed in Table 36„ -187= TABLE 36 GENERAL FEATURES OF TWO SIZES OF DAM AND RESERVOIR AT THE SAN MIGUELITO SITE ON NACIMIENTO RIVER Characteristics of Site Drainage area-~68oii square miles Estimated average seasonal runoff —50,800 acre-feet Estimated average net seasonal depth of evaporation- -2. 82 feet Estimated sedimentation- -1 5 000 acre-feet Elevation of stream bed, U.S.G.S datum—1,110 feet jGross reservoir storage capacity, : in acre-feet 50,000 130,000 Earthfill Dam Crest elevation, in feet, U0S.G0S. datum 1,250 1,285 Crest length, in feet U80 630 Crest width, in feet 30 30 Height, spillway lip above stream bed, in feet 126 158 Side slopes, upstream and downstream 2.5sl 3*1 Freeboard, above spillway lip, in feet 111 17 Volume of fill, in cubic yards 638,200 1,300,000 Saddle Dams Number of dams 2 Aggregate crest length, in feet 2,7UO Height, in feet 50 Crest width, in feet 30 Side slopes _— 2,5sl Total volume of fill, in cubic yards — 103,800 Reservoir Surface area at spillway lip, in acres 1,820 3,060 Net storage capacity at spillway lip, in acre-feet IjQ, 000 129,000 Type of spillway Ogee weir located in saddle Spillway discharge capacity, in second feet Ii9,000 38,600 Type of outlet 30-inch 36-inch diameter diameter steel pipe steel pipe Estimated net safe seasonal yield, in acre-feet 6,000 13,000 -188- GENERAL FEATURES OF TWO SIZES OF DAM AND RESERVOIR AT THE SAN MIGUELITO SITE ON NACIMIENTO RIVER (continued) sGross reservoir storage capacity, s in acre-feet 50,000 8 130,000 Capital Costs Dam and reservoir $L,73k,OQO 13,017,000 Per acre-foot of storage 35 23 Per acre-foot of net safe yield 289 232 Annual Costs Dam and reservoir $ 88,700 $ 155*600 Per acre-foot of net safe yield 11* ,80 12,00 Per acre°foot of incremental net safe yield 9c60 -189- For each height of dam, the earthfill structure would comprise an impervious core of select earth material , and upstream and downstream sections of pervious free-draining material . The upstream face of the dam would be protected against wave action by rock riprap placed to a depth of three feet normal to the slope. Earthfill material suitable for the impervious section of the dam could be obtained from within the reservoir area. It is estimated that about 80 per cent of the spoils could be salvaged for use as riprap and in the pervious section of the dam For the reservoir of 130,000 acre-feet capacity, two auxiliary dams would be required in the saddles about one mile north of the main dam site. The auxiliary dams would consist of rolled earth sections. The faces of the auxiliary dams on the reservoir side would be protected with a three-foot depth of rock riprap. It is estimated that an average of about six feet of residual soil and weathered bedrock would have to be stripped under the auxiliary dams. Spillways for the 50,000 and 130,000 acre-feet capacity reservoirs would have discharge capacities of 1j9c,000 and 38,600 second-feet, respectively. They would be designed as concrete-lined overpour chutes, located near the afore-mentioned saddle dams and would discharge into Gabilan Creek. Outlet works for either height of dam would consist of submerged concrete intake structures with trash racks located near the right abutment at the upstream toe of the dam. Releases would be controlled by a 3»5 x 3«5-foot high pressure slide gate located in a gate chamber at the center of the dam. A concrete pressure conduit beneath the dam, founded on bedrock, would extend from the inlet tower to the valve chamber located at the axis of the dam. A reinforced concrete pipe would extend from the valve chamber to the control valve house and would house an access passageway to the valve chamber as well as a steel outlet pipe supported on cradles. Downstream releases -190- „ „ , would be further regulated by Howell =Bunger valves It was estimated that either height of dam could be constructed within one year and that summer flow of Nacimiento River could be diverted through the outlet works As the dam and reservoir land is owned by the Federal Government a nominal cost for land acquisition of $10 per acre was assumed,, An access road from the "San Miguelito Loop Road" (Military) would have to be con- structed for a distance of about two miles to furnish access to the main dam site Jarre tt Shut-In Dam and Reservoir The Jarrett Shut-In dam site is located in Monterey County on the Nacimiento River 5 near the center of the west half of Section 19, Township 21* South, Range 8 East, M D B & M„ The site is located some 37 miles upstream from its confluence with the Salinas River and about nine miles downstream from the San Miguelito dam site,, The reservoir area is partially within the Hunter Liggett Military Reservation and partially within the Los Padres National Forest, The main dam site is on the boundary between the military reservation and privately owned lands The site of a saddle dam that would contain the spillway is located within the military reservation Water passing over the spillway would pass through the military as well as privately owned lands along El Piojo Creek before returning to the Nacimiento River,, The main dam site is characterized by a spectacularly narrow gorge Consideration was given to construction of a dam and reservoir at the Jarrett Shut-In site for storage of surplus waters of the Nacimiento River, and utilization of the waters so conserved in the Upper Salinas Unito =191- The Jarrett Shut-In dam and saddle dam sites were mapped at a scale of one inch equals 100 feet, with contour interval of 10 feet, by the Division of Water Resources in 19£iu Reservoir areas and storage capacities for various stages of water surface elevation were computed from U. S. Geological Survey quadrangles at a scale of ls2U,000, with contour interval of 20 feet, and are shown in Table 37» -192- TABLE 37 AREAS AND CAPACITIES OF JARRETT SHUT-IN RESERVOIR Depth Water surface ; Water s Storage of water i : elevation, : surface : capacity, at dam, : UoSoGoSo datum, j area 5 : in in feet ! in feet : in acres s acre-feet 900 10 910 3 20 20 920 10 80 30 930 28 270 ko 9U0 51* 680 50 950 79 1,350 60 960 110 2,290 70 970 IliO 3,51*0 80 980 190 5,190 90 990 250 7,390 100 1,000 320 10,200 110 1,010 380 13,700 120 1,020 1*30 17,800 130 1,030 5io 22,500 IliO 1,01*0 580 27,900 11*1* i,oid* 610 30,000 150 1,050 660 3i*,100 160 1,060 760 111, 200 170 1,070 880 1*9,1*00 180 1,080 1,01*0 59,000 190 1,090 1,270 70,600 193 1,093 1,350 75,000 200 1,100 1,570 81*, 800 210 1,110 1,850 102,000 21U 1,111* 1,960 110,000 220 1,120 2,130 122,000 230 1,130 2,610 il*5,5oo 21*0 1,11*0 3,090 171*, ooo 250 1,150 3,620 207,500 260 1,160 1*,170 2146,500 270 1,170 1*,720 291,000 280 1,180 5,270 31*1,000 290 1,190 5,91*0 397,ooo 300 1,200 6,730 li60,000 -193- Preliminary geologic reconnaissance by the Division of Water Resources in 1953 indicated that the Jarrett Shut-in dam site is suitable for either a gravity or arch type of dam. The maximum feasible height of dam is limited by a broad saddle occurring within the reservoir area approximately 1,5 miles northwest of the dam site. The abutment slopes at the dam site vary from nearly vertical to 1,25 to 1, with the average slope about 0.75 to 1, Shaping of the abutments would be required for construction of an earthfill dam The foundation rock at the dam site consists of a massively bedded, weather-resistant cobble conglomerate of Cretaceous age. The individual cobbles of the mass are invariably sheared and recemented. The rock is hard and well cemented, and the ground mass consists of medium to coarse-grained, poorly sorted sandstone, A few very blocky joints divide the bedrock mass. No major faults or shears were observed on the abutments, but there is evidence of possible major faulting passing through the gorge in the channel section. No exploratory drilling is known to have been done at the site, and a drilling program should be accomplished prior to any final considera- tion for construction of a darn. Yield studies were made for reservoir storage capacities of 30,000 acre-feet, 75i>000 acre-feet, and 110,000 acre-feet at the Jarrett Shut-in site, and are summarized in Appendix K„ The estimates of safe seasonal yield obtained from these studies, with Jarrett Shut-in Reservoir operated as a secondary development coordinately with existing Nacimiento Reservoir, were as follows s -19)4= < Gross reservoir Safe seasonal Height of storage yield, in main darn, capacity, acre-feet in feet in acre-feet Gross : Net 163 30,000 7,700 6,000 213 75 5 ooo 13,500 10, £00 233 110,000 17*600 13,800 Differences between gross and net yields presented in the foregoing tabulation represent releases required to maintain water levels in the down- stream ground water basins at elevations which would prevail with reservoir operation,, The relationship between reservoir storage capacity and net safe seasonal yield for Jarrett Shut-In Reservoir is shown graphically on Plate 22 After consideration of results of the yield studies, geologic reconnaissance, and topography of the site, detailed estimates of cost were prepared for a main concrete arch dam, auxiliary earthfill saddle dams, and reservoir of each of the foregoing three sizes, which estimates are presented in Appendix L General features of the three sizes of dam and reservoir are listed in Table 38 =195- TABLE 38 GENERAL FEATURES OF THREE SIZES OF DAM AND RESERVOIR AT THE JAHRETT SHUT-IN SITE ON NACIMIENTO RIVER Characteristics of Site Drainage area-=130 square miles Estimated average seasonal runoff—95,200 acre-feet Estimated average net seasonal depth of evaporation— 2*82 feet Estimated sedimentation— 2,000 acre-feet Elevation of stream bed, U.SoG.S. datum—900 feet :Gross reservoir storage capacity, : in acre-feet 30,000 7T,Q00 110,000 Arch Dam Crest elevation, in feet, U.S.G.S. datum 1,063 1,113 1,133 Crest length, in feet 1*02 U67 522 Crest width, in feet 6 6.5 7 Height, spillway lip above stream bed, in feet 193 21J4 Freeboard, above spillway lip, in feet 19 20 19 Volume of concrete, in cubic yards 17,800 U5,ooo 5U,ooo Auxiliary Saddle Dams Number of saddle dams 1 2 Aggregate crest length, in feet 1,910 2,350 Height, in feet 85 105 Crest width, in feet 20 20 Side slopes 2,5:1 2.5:1 Total volume of fill, in cubic yards 576,000 1,102,000 Reservoir Surface area at spillway lip, in acres 610 1,350 1,960 Net storage capacity at spillway lip, in acre-feet 28,000 73,000 108,000 Type of spillway Ogee weir with concrete chute Spillway discharge capacity, in second feet 75,ooo 71,600 70,000 Type of outlet 36-inch Two 30- and diameter 30-inch 36-inch steel diameter diameter pipe steel steel pipes pipes Estimated net safe seasonal yield, in acre-feet 6,000 10,500 13,800 -196- GENERAL FEATURES OF THREE SIZES OF DAM AND RESERVOIR AT THE JARRETT SHUT-IN SITE ON NACIMIENTO RIVER (continued) sGross reservoir storage capacity,, : in acre-feet s_ 30 , QQQ % 75,000 j 110,000 Capital (£ost Dam and reservoir $1,736,000 $3,7143,000 $1^,691,000 Per acre=foot of storage 58 50 U3 Per acre-foot of net safe yield 289 356 3U0 Annual Cost Dam and reservoir 86,800 185,300 232,700 Per acre-foot of net safe yield 11**50 17.60 16.90 Per acre-foot of incremental net safe yield 21.90 ihoko =197- The main dam was designed as a concrete arch of the variable radius and variable angle type, in order to best fit the topography of the site» A dam more than 220 feet in height would probably require a thrust block at the left abutmento In view of the lack of data concerning foundation condi- tions g a depth of 1$ feet normal to the surface was assumed for stripping at the main dam Subsurface exploration by slant core drilling would be necessary to determine the nature and structure of the underlying bedrock with regard to its suitability as foundation for an arch darn, and to determine the depth of debris in the channel section,. For cost estimating purposes a unit cost of $20 < per cubic yard for concrete in the arch dam was assumed, on the premise that local aggregates would be used with low alkali cement Aggregates downstream along the Nacimiento River have been used by the State Division of Highways for concrete structures, and appear to meet their specifications in regard to sodium sulfate soundness and Los Angeles Rattler tests o Further testing of the aggregates for reactiveness and soundness would be necessary before their use in construction of an arch dam at this site* In the event local aggregates should prove to be not suitable for an arch dam, it might be more economical to construct an earthfill dam rather than import more expensive aggregates from a proven source,. A preliminary estimate indicated that the cost of an earthfill dam creating a reservoir storage capacity of 75,000 acre-feet would be comparable to the cost of an arch dam at this site» Auxiliary earthfill dams would be required in the saddle to the northwest of the main dam site for the 75,000 and 110,000 acre-foot capacity reservoirs o Although an auxiliary dam would not be required for the 30,000 acre-foot reservoir, small slab and buttress dams were designed to close the saddle on both sides of the spillway. In the design of the two -198- • auxiliary dams required for the 110,000 acre-foot reservoir 9 the earthfill would abut on either side of the reinforced-concrete spillway training wallso The upstream faces of the dams would be protected against wave action by rock riprap placed to a depth of three feet normal to the slope a Under the impervious section of the auxiliary dams^, an average depth of stripping of 10 feet was assumed,, The capacity of the reservoir is considered limited to 110^,000 acre-feet at the Jarrett Shut-In site since (l) sufficient earthfill materials are not available within a reasonable haul distance for construction of large saddle dams, (2) thrust blocks would be necessary at the abutments to accom- modate a higher arch dam s and (3) there is no saddle suitable for a spillway for a higher dam The spillway was designed as a concrete-lined overpour chute with an ogee weir control section placed through the saddle northwest of the main dam site and discharging into El Piojo Creek, No provision was made for overpour at the arch 2 due to the height of the dam and the character of the foundation rock The estimated construction time for heights of dam with reservoir storage capacities of 30 5 000 acre-feet 5 7£ 5 000 acre-feet, and 110,000 acre- feet;, would be one,, two,, and three years 5 respectively,. Diversion of the stream during construction would be accomplished through the outlet works during summer months 9 and through a depressed section of the arch dam during winter months Outlet works in each instance would consist of a steel pipe placed through the main dam Releases would be controlled by high-pressure slide gates located on the upstream face of the dam and protected by trash rack structures o The releases would be further controlled by Howell-Bunger valves -199- located on the downstream face of the dam If the releases from the reservoir were to be used for domestic purposes 9 an intake tower could be constructed on the upstream face of the dam As has been stated, the Jarrett Shut-in reservoir area is in the Los Padres National Forest and the Hunter Liggett Military Reservation, The only improvements which would probably require relocation are a few miles of military roads and telephone lines of temporary type of construction. It was assumed that the road over the ridge to State Highway No, 1 at San Simeon would not require relocation because it is not a through road for public travelo Considerable clearing of the reservoir lands would be required, A new all-weather road from the paved "Sam Jones" military road would have to be constructed for a distance of about 3<,5> miles to furnish access to the dam sites. For illustrative purposes , the plans , profiles, and sections for the arch dam and saddle dam creating a reservoir with storage capacity of 110,000 acre-feet at the Jarrett Shut-In site are shown on Plate l£<> Bald Top Dam and Reservoir , The Bald Top dam site is located on San Carpoforo (San Carpojo) Creek about six miles upstream from its mouth and about four miles upstream from the Upper Ragged Point site, in the south- west quarter of Section 36, Township 2\\ South, Range 6 East, M, D, B, & M, The San Luis Obispo-Monterey county line passes through the site. Consider- ation was given to construction of a dam and reservoir at the Bald Top site for storage of flood waters in San Carpoforo Creek and utilization of the waters so conserved in the Coastal Unit, The Bald Top dam site and reservoir area are shown on a U. S. Geological Survey quadrangle at a scale of 1:2U,000, with a contour interval =200= of 20 feeto The quadrangle was enlarged photographically to a scale of one inch equals 5>00 feet for dam layout and cost estimating purposeso Reservoir areas and storage capacities for various stages of water surface elevation were computed from this map and are presented in Table 39o =201= TABLE 39 AREAS AND CAPACITIES OF BALD TOP RESERVOIR Depth Water surface s Water s Storage of water : : elevation, s surface § capacity, at dam,, : : U.SoG.S. datum. ; area , % in °. in feet : in feet in acres i acre-feet 670 10 680 2 10 20 690 8 60 30 700 19 200 Uo 710 29 hho 50 720 h2 790 60 730 58 1,290 70 7U0 76 1,960 80 750 99 2,8UO 90 760 120 3,930 100 770 liiO 5,230 110 780 150 6,680 120 790 170 8,280 130 800 180 10,000 liiO 810 200 11,900 150 820 210 lii,000 160 830 230 16,200 170 8U0 21*0 18,500 175 Qh5 250 19,700 180 850 260 21,000 190 860 270 23,700 200 870 290 26,500 210 880 300 29,1*00 220 890 320 32,500 230 900 330 35,800 •202- o Based upon preliminary geologic reconnaissance 9 the Bald Top dam site is considered suitable for an earthfill dam of moderate height Geology of the site was investigated by the Division of Water Resources in 195U° No exploratory drilling or trenching of the foundation areas has been done at this site nor of the borrow areas Bedrock consists of siltstone^ shale s and sandstone » Although rocks are poorly exposed at the site a they appear to dip upstream Exposures show that the sediments have been highly fractured and both quartz and calcite veins were notedo Near the upstream toe of the dam 5 shales have formed small slides near the stream bed 5 but no large slides were foundo The rocks would probably take moderate groutingo Stripping under the impervious section of the dam on both abutments is estimated to be about three feet of soil and 10 feet of loose rock In the channel section of the dam 5 it is estimated that an average of 20 feet of gravel and boulders and five feet of loose rock would have to be stripped under the impervious core c A nominal depth of stripping of two feet may be required under the random fill sections A yield study was made for a reservoir storage capacity of 20,000 acre-feet at the Bald Top siteo Results of that study s which are presented in Appendix K 9 show that a dam 175 feet high 5 impounding 20^000 acre-feet of water j, would produce both a gross and net safe seasonal yield of 10«,U00 acre-feet when operated as a primary development on San Carpoforo Creeko Gross and net yields were assumed to be equal since it is believed that storage of flood flows at the Bald Top site would have no appreciable effect on recharge of San Carpoforo Basin c Furthermore,;, it will be shown subse- quently that soils comprising the irrigable lands overlying the San Carpoforo Basin will either be inundated or be required for construction of the Upper -203= „ Ragged Point Dam and Reservoir e The relationship between reservoir storage capacity and net safe seasonal yield for Bald Top Reservoir is shown on Plate 22 After consideration of results of yield studies , geologic recon- naissance, and availability of materials, a detailed estimate of cost was prepared for an earthfill dam and reservoir having a storage capacity of 20,000 acre-feet s which estimate is presented in Appendix L General features of the dam and reservoir are presented in Table k0« =20U- , TABLE kO GENERAL FEATURES OF A DAM AND RESERVOIR AT THE BALD TOP SITE ON SAN CARPOFORO CREEK Characteristics of Site Drainage area— 15 square miles Estimated average s easonal runoff —18,500 acre-feet Estimated average net seasonal depth of evaporation--! «>5U feet Estimated sedimentation—500 acre-feet Elevation of stream bed, U.SoG=S datum—670 feet ;Gross reservoir storage capacity in acre-feet ; s 20,000 Barthfill Dam Crest elevation^, in feet, UoSoGoSo datum 860 Crest length., in feet 960 Crest widths in feet 30 Height , spillway lip above stream bed, in feet 175 Side slopes, upstream and downstream 3:1 Freeboard , above spillway lip, in feet 15 Volume of fill, in cubic yards 1,528,900 Reservoir Surface area at spillway lip, in acres 250 Net storage capacity at spillway lip, in acre-feet 19,500 Type of spillway Chute Spillway discharge capacity, in second-feet 7,600 Type of outlet 30-inch diameter steel pipe Estimated net safe seasonal yield, in acre -feet 10.U00 Capital Costs Dam and reservoir $2,2U9,000 Per acre-foot of storage 112 Per acre-foot of net safe yield 216 Annual Costs Dam and reservoir $111,300 Per acre-foot of net safe yield 10,70 =205- The earthfill structure would comprise an impervious core of select material, and upstream and downstream sections of random fill material. The upstream face of the dam would be protected against wave action by rock riprap placed to a depth of three feet normal to the slope. Boulders in the stream bed and massive sandstones near the dam site may furnish sufficient material for this purpose. It was estimated that there are possibly £00 5 000 cubic yards of impervious material in the reservoir area. Random fill material could be obtained from the reservoir area and from salvage of excavated materials. Employment of semipervious random fill would necessitate installa- tion of a gravel blanket and drains along the downstream face of the impervious section to carry away any water seeping through the impervious core. The concrete-lined spillway would be located on the left abutment and was designed as the chute type with an ogee weir control section. The spillway would have a discharge capacity of 7 9 600 second-feet and would dis- charge into San Carpoforo Creek about l£0 feet downstream from the toe of the dam. The concrete intake structure for the outlet works would be located at the upstream toe of the dam near the right abutment with a steel trash rack at its entrance, A concrete pressure conduit beneath the dam would extend from the intake to a gate chamber located slightly upstream of the dam axis s wherein a high pressure slide gate would be installed, A reinforced- concrete pipe^, founded on bedrock 9 would extend beneath the dam from the gate chamber to the valve house 9 and would contain an access passageway to the gate chamber as well as a steel outlet pipe. The outlet pipe would have a diameter of 30 inches. It was estimated that the dam could be constructed within one year, and that summer flow of San Carpoforo Creek could be diverted through the outlet conduit during construction, -=206- , Construction of an access road would be required for a distance of about 5>ol miles o The only improvement in the reservoir area is a small summer cabin. Upper Ragged Point Dam and Reservoir . The Upper Ragged Point dam site is located on San Carpoforo (San Carpojo) Creek;, about l a 8 miles from its mouthy and on the line between Sections lij. and l$ s Township 2£ south Range 6 east, M D, B & M Stream bed elevation at the site is about 70 feet, UoSoGoSo datum Consideration was given to construction of a dam and reservoir at the Upper Ragged Point site for storage of surplus waters of San Carpoforo Creeks and utilization of the waters so conserved in the Cambria and San Luis Obispo Subunits of the Coastal Unit a The Upper Ragged Point dam site and reservoir area are shown on a U So Geological Survey quadrangle at a scale of 152115000^, with a contour interval of 20 feet Since the dam site has not been mapped, the quadrangle was enlarged photographically to a scale of one inch equals 500 feet for dam layout and cost estimating purposes o Reservoir areas and storage capacities for various stages of water surface elevation were computed from this map and are presented in Table Ulo =207= TABLE ill AREAS AND CAPACITIES OF UPPER RAGGED POINT RESERVOIR Depth : Water surface : Water : Storage of water : elevation, : surface : capacity, ' at dam, ! U.S.G.S. datum, 1 area, : in in feet i ! in feet 2 in acres 5 acre-feet 70 10 80 8 30 20 90 28 210 30 100 50 600 UO 110 62 1,160 50 120 70 1,820 60 130 78 2,560 70 LUO 86 3,380 80 150 9k U,280 90 160 100 5,250 100 170 110 6,300 110 180 120 7,U50 120 190 135 8,720 130 200 150 10,200 lUo 210 160 11,700 150 220 170 13 5 i;00 160 230 175 15,100 170 2U0 180 16,800 180 250 195 18,700 190 260 210 20,800 200 270 220 22,900 210 280 230 25,200 220 290 2U0 27,500 230 300 255 30,000 2U0 310 270 32,600 250 320 280 35AOO 260 330 290 38,200 270 3W 305 hi, 200 280 350 320 ill;, 300 290 360 330 U7,600 300 370 3U5 50,900 310 380 360 5^00 320 390 380 58,200 330 UOO Uoo 62,000 -208= o „ Based upon preliminary geologic reconnaissance^ the Upper Ragged Point dam site is considered suitable for an earthfill dam of moderate height Geology of the site was investigated by the Division of Water Resources in 1955 o No exploratory drilling or trenching of the foundation has been done at this sitec, nor of the borrow areas Bedrock at the site consists of well cemented sandstone and silt- stone 9 sheared shale s and some metavolcanicso It is highly fractured and jointed 5 and heavy grouting would be required* The State Geologic Map shows a large fault about three-fourths mile southwest of the site. There is a small rubble slide on the left abutment and some talus near the base of the right abutment In the channel section of the dam 5 an average estimated depth of 25 feet of gravel and three feet of loose bedrock would have to be stripped under the impervious core. On the left and right abutments , an estimated two feet of soil and five feet of loose rock would have to be removed under the impervious section for the first 200 feet of dam height » Above 200 feet of dam heights about four feet of soil^ and five feet of loose rock would have to be removed. Removal of the slide and talus material would also be neces- sary,, For the pervious fill sections s a nominal depth of stripping of two feet may be required throughout the contact area A yield study was made for a reservoir storage capacity of 30 , 000 acre-feet at the Upper Ragged Point site Results of that study are presented in Appendix K and show that a dam 230 feet highj, impounding 30 5 000 acre-feet of water 5 would produce gross and net safe seasonal yields of 17 5 500 acre= feet when operated as a primary development on San Carpoforo Creek „ The foregoing gross and net yields were assumed to be equal since all of the irrigable valley lands overlying the San Carpoforo Basin shown on Plate 11B =209-= would either be inundated by the reservoir or would be used as construction materials for Upper Ragged Point Dam,, A conjunctive operation study was also made for reservoirs at both the Bald Top and Upper Ragged Point sites. Results of the latter study show that a reservoir with 20,000 acre-feet of storage at the Bald Top site operated coordinately with a reservoir with 30,000 acre-feet of storage at the Upper Ragged Point site would produce a gross and net safe system yield of 22,^00 acre -feet per season. The relationship between storage capacity and net safe seasonal yield for Upper Ragged Point Reservoir and also for the combined Upper Ragged Point and Bald Top Reservoirs is shown on Plate 22. After consideration of the results of yield studies, geologic reconnaissance, and topography of the site, preliminary estimates of cost were prepared for an earthfill dam and reservoir having a storage capacity of 30,000 acre-feet, which estimate is presented in Appendix L„ General features of the dam and reservoir are presented in Table U2« -210- TABLE U2 GENERAL FEATURES OF A DAM AND RESERVOIR AT THE UPPER RAGGED POINT SITE ON SAN CARPOFORO CREEK Characteristics of Site Drainage area~-3Uo3 square miles Estimated average seasonal runoff—36,600 acre-feet Estimated average net seasonal depth of evaporation—1<,5U feet Estimated sedimentation~-500 acre-feet Elevation of stream bed, U S G<,So datum— 70 feet sGross reservoir storage capacity, : in acre -feet 30,000 Earthfill Dam Crest elevation j in feet, UoS o G S datum 320 Crest lengthy in feet 1*010 Crest widths in feet 30 Height, spillway lip above stream bed g in feet 230 Side slopes, upstream and downstream 3 si Freeboard, above spillway lip, in feet 20 Volume of fill, in cubic yards k> 006,500 Surface area at spillway lip, in acres 255 Net storage capacity at spillway lip, in acre-feet 29*500 Type of spillway Chute Spillway discharge capacity, in second-feet 15,000 Type of outlet U2-inch diameter steel pipe Estimated net safe seasonal yield, in acre-feet 17,500 Capital Costs Dam and reservoir $5*1*20,000 Per acre-foot of storage 181 Per acre-foot of net safe yield 310 Annual Costs Dam and reservoir $259,800 Per acre-foot of net safe yield lU o 80 =211= The earthfill structure would comprise an impervious core of select material, and upstream and downstream sections of pervious free draining material o Adequate quantities of fill material are not available in the proposed reservoir area 9 It is estimated that additional material suitable for use in the impervious section of the dam could be obtained from terraces to the southwest of the site within about 1*8 miles of haul distance,, Additional pervious fill material could be obtained from the stream channel downstream from the dam site* The upstream face of the dam would be pro- tected against wave action by rock riprap placed to a depth of three feet normal to the slope Riprap could be quarried from hard outcrops located about three miles upstream from the site© The concrete=lined spillway would be located on the right abutment and was designed as the chute-type with an ogee-weir control section,. The spillway would have a discharge capacity of 15 3 000 second-feet and would dis- charge into San Carpoforo Creek about 3>00 feet downstream from the toe of the dam. A pilot channel or other special treatment would be required at the approach to the spillway to prevent the flood discharge of a large ravine from eroding the upstream face of the dam a The outlet works would have a concrete intake structure located at the upstream toe of the dam near the left abutment and a steel trash rack at its entrances A concrete pressure conduit beneath the dam would extend from the intake to a gate chamber located slightly upstream of the axis of the dam, wherein a high pressure slide gate would be installed. A reinforced- concrete culvert, founded on bedrock s would extend beneath the dam from the gate chamber to the valve house It would contain an access passageway to the gate chamber as well as a steel outlet pipe, 1*2 inches in diameter, supported on cradles »212- It was estimated that the dam could be constructed in two years and diversion of the summer flows of San Carpoforo Creek during construction could be effected through the outlet conduito Diversion of winter flows would be effected through a closure section,, As the channel is rather narrow at the site s a large amount of fill would need to be placed the second year<> Included in the reservoir area are an abandoned ranch house and two barns o There is also an access road to an abandoned quicksilver mine which would be relocated,, Yellow Hill Dam and Reservoir Q The Yellow Hill dam site is located on Arroyo de la Cruz about 1<>5> miles upstream from its mouth in the Piedra Blanca Land Granto A site suitable for a small dam and reservoir is located about 0„5 mile upstream and is called Upper Yellow Hill dam site Considera- tion was given to the construction of dams and reservoirs at both of the two sites described for storage of flood waters of Arroyo de la Cruz and utiliza- tion of waters so conserved in the Cambria and San Luis Obispo Subunits of the Coastal Hydrologic Unite The Yellow Hill reservoir area was mapped in 1955 utilizing photo- grammetric methods by the Division of Water Resources at a scale of one inch equals 500 feet with a 25~foot contour interval Topography was carried up to a minimum elevation of 200 feeto Reservo ir areas and storage capacities computed from this map for the Upper Yellow Hill and Yellow Hill sites are presented in Tables U3 and UU a respectively,. The dam sites were mapped photogrammetrically at a scale of one inch equals 500 feet with a contour interval of 20 feet to an elevation of 300 feeto 213= TABLE U3 AREAS AND CAPACITIES OF YELLOW HILL RESERVOIR Upper Site Depth i Water surface Water Storage of water : ! elevation, i : surface : ! capacity, at dam, : i U.S.G. S. datum, ! area, ' i- n in feet : in feet in acres acre-feet Uo 10 50 51 170 20 60 88 860 30 70 130 1,960 UO 80 170 3,1*50 50 90 220 5,Uoo 60 100 280 7,900 70 110 320 10,900 80 120 360 1)4,300 90 130 iiOO 18,100 9$ 135 Uio 20,100 100 lilO U20 22,200 110 150 U50 26,600 -21U- TABLE UU AREAS AND CAPACITIES OF YELLOW HILL RESERVOIR Lower Site Depth ! Water surface s Water : Storage of water : i elevation, ; surface : capacity, at dam, : U.S.G.S. datum,, ; area, z in ° in feet 5 in feet in acres t acre»feet 30 10 ko U9 160 20 50 97 890 30 60 lilO 2,080 Uo 70 180 3,680 50 80 230 5,730 60 90 280 8,280 70 100 3U0 ll,i|00 80 110 kOO 15,100 90 120 Uho 19,300 100 130 h80 23,900 110 mo 510 28,800 120 150 5U0 3li,100 130 160 570 39 , 600 11*0 170 600 1+5,500 1U7 177 620 1*9,800 150 180 6U0 51,700 160 190 680 58,300 170 200 710 65,200 180 210 750 72,500 190 220 790 80,200 200 230 830 88,300 210 2i|0 870 96,800 220 250 910 105,700 •215- : A geologic investigation of the Yellow Hill dam site was made in 195U by the geologists of the Division of Water Resources o No prior geologic work at this site is known, nor have the foundation and borrow areas been explored by drilling,, The site appears to be suitable for a moderately high earthfill dam« Bedrock consists of altered volcanic rock which weathers to a red soil. The volcanics have been locally serpentinized and very highly fracturedo A large fault zone crosses the stream bed about 600 feet above the axis of the dam and dips about 60 degrees toward the ocean „ Although the impervious section of the dam would not reach this fault zone, suitable design precautions would be necessary to insure the stability of the dam„ The bed- rock at the site would probably require moderate to heavy grouting. Stripping on both abutments under the impervious section of an earthfill dam at this site was estimated to average about five feet of soil and 20 feet of loose rocko In the channel section an estimated average depth of about liO feet, with a possible maximum of 60 feet, of gravel would have to be stripped under the impervious core of a dam. Yield studies were made for reservoir storage capacities of 20,000, 50,000, and 80,000 acre-feet at the Yellow Hill sites. Detailed results of these studies are presented in Appendix K„ Estimates of safe seasonal yield obtained from the studies are as follows Gross reservoir Safe seasonal Height storage yield, of dam, capacity, in acre -feet in feet in acre-feet Gross : Net 95 20,000 13 5 500 13,100 1U7 50,000 23,300 22,900 190 80,000 27,700 27,300 -216= „ The difference of 1*00 acre-feet between gross and net yields presented in the foregoing tabulation represents the probable ultimate mean seasonal water requirement of lands overlying Arroyo de la Cruz Basin which would not be affected by the construction of the dam and reservoir <> The relationship between reservoir storage capacity and net safe seasonal yield for Yellow Hill reservoir is shown graphically on Plate 22 As a result of the geological investigation and the reservoir yield studies, estimates of cost were prepared for dams at the Yellow Hill site with heights of lli7 and 190 feet from stream bed to spillway lip, creating reservoir capacities of 5>0,000 and 80,000 acre-feet, respectively,, An estimate of cost was also prepared for a dam at the Upper Yellow Hill site with a height of 95 feet from stream bed to spillway lip and creating a reservoir storage capacity of 20,000 acre-feeto Detailed estimates of cost for the three foregoing reservoir capacities are presented in Appendix L, and general features of the three dams and reservoirs are listed in Table k%<> •217- TABLE 1*5 GENERAL FEATURES OF THREE SIZES OF DAM AND RESERVOIR AT THE YELLOW HILL SITE ON ARROYO DE LA CRUZ Characteristics of Site Drainage area— 1*1<>1* square miles Estimated average seasonal runof f—Uii^800 acre-feet Estimated average net seasonal depth of evaporation— 1-51* feet Estimated sedimentation—1,000 acre-feet Elevation of stream bed, U.S.G.S. datum—l*0 and 30 feet sGross reservoir storage capacity, t in acre-feet 20,000 s 50,000 s 60,000 Earthfili Dam Crest elevation, in feet, U.S.G.So datum 150 192 231* Crest length, in feet 980 1,030 1A30 Crest width, in feet 30 30 30 Height, spillway lip above stream bed, in feet 95 11*7 190 Side slopes, upstream and downstream 2„5sl 2o5sl 3:1 Freeboard, above spillway lip, in feet 15 15 11* Volume of fill, in cubic yards 869,900 2,11*2,500 1*, 228, 100 Reservoir Surface area at spillway lip, in acres 1*10 620 790 Net storage capacity at spillway lip, in acre-feet 19,000 1*9,000 79,000 Type of spillway Ogee weir with concrete-lined chute Spillway discharge capacity, in second~feet 16, 200 13,900 11,900 f Type of outlet 30- inch l*8-inch 60-inch diameter diameter diameter steel steel steel pipe pipe pipe Estimated net safe seasonal yield, in acre-feet 13,100 22,900 27,300 Capital Costs Dam and reservoir $1,1*20,000 $3,599,000 $6,1*01,000 Per acre-foot of storage 71 ,72 .80 Per acre-foot of net safe yield 108 157 231* Annual Costs Dam and reservoir $71,500 $176,100 $310,200 Per acre-foot of net safe yield 5»50 7.70 11.1*0 Per acre-foot of incremental net safe yield 10.70 30.50 -218- „ For all heights of dam 5 earthfill structures were contemplated comprising an impervious core of select earth material with upstream and downstream sections of random semipervious material „ The upstream face of the dam would be protected against wave action by rock riprap placed to a depth of three feet normal to the si ope „ Employment of semipervious random fill in the outer sections would necessitate the installation of gravel blankets and drains along the downstream face of the impervious core as a precautionary measure to carry away possible leakage that might occur through the impervious section and at the abutments It was assumed that 75 per cent of the material excavated from channel and abutments could be used in the random fill section of the dam„ Stream gravels and bedrock could also be used as random fillo Rock for rip- rap could be obtained from a quarry about six miles upstream „ Impervious material does not appear to be available in adequate quantities in the alluvium of the reservoir area. The alluvial flats downstream from the pro- posed dam contain only a foot or two of soil and this would probably not be workable,. The weathered volcanic rock may furnish adequate impervious material but testing would be required to determine its suitability,, For cost estimating purposes , it was assumed that additional impervious material would be obtained from terrace deposits along the edge of the ocean westerly s and to the north and south of the site along State Highway No 1» At present these terraces are used mostly for grazing and a cost for acquisition of this land for borrow material was taken into account in cost estimates <, However,, it should be noted that if development occurs along this coastal area, the value of the land may be substantially increased,, The spillway was designed as a concrete-lined chute with ogee weir control sections „ The spillway would be excavated through the right -219= ° „ „ abutment and discharge into a small ravine discharging into Arroyo de la Cruz just downstream from the dam Riprap protection was provided on the downstream toe of the dam near where the ravine discharges into Arroyo de la Cruz. At the site for the smaller dam upstream, a spillway could be excavated through a ridge on the left abutment, and a small saddle dam would be required to the left of this spillway,, The spillway for the 80,000 acre-foot reservoir would have a discharge capacity of 11,900 second- feet » The outlet works would be located on the left abutment,, The intake structure would consist of a short concrete tower with a steel trash rack at its entrance,, A concrete pressure conduit would be installed beneath the dam and would extend from the intake to a gate chamber located slightly upstream from the axis of the dam, wherein a high pressure slide gate would be in- stalled,, A reinforced-concrete culvert, founded on bedrock, would extend beneath the dam from the gate chamber to a valve house located at the down- stream toe of the dam This culvert would house an access passageway to the gate chamber as well as a steel outlet pipe supported on cradles. This pipe would have a diameter of 60 inches* Releases would be regulated by a Howell-Bunger and a needle valve It was estimated that the dam for the largest size of reservoir could be constructed in two years, and summer flow of Arroyo de la Cruz could be diverted through the outlet conduit. This dam could be so constructed as to allow a closure section of the earthfill embankment to accommodate winter flows during the first winter There are no county roads in the reservoir area,, Improvements include a few irrigation wells and an abandoned ranch For illustrative purposes, the plan, profile, and section for the dam creating a reservoir with storage capacity of 80,000 acre-feet at the =220- Yellow Hill site are shown on Plate 18 San Simeon Dam and Reservoir., The San Simeon dam site is located in the San Simeon Land Grant on San Simeon Creek about two miles upstream from its moutho Consideration was given to the construction of a dam and reservoir at the San Simeon site for storage of floodwaters in San Simeon Creek and utilization of waters so conserved in the Cambria and San Luis Obispo Subunits of the Coastal Unit G The San Simeon dam site and reservoir area was mapped at a scale of one inch equals 500 feet with a contour interval of 25 feet by the Division of Water Resources in 1955 using photogrammetric methods Reservoir areas and storage capacities for various water surface elevations computed from this reservoir map are presented in Table if.6 =221= TABLE 1*6 AREAS AND CAPACITIES OF SAN SIMEON RESERVOIR Depth Water surface : Water s Storage of water s elevation, % surface : capacity, at dam, \ UoSoGoSc datum, s area, 1 in in feet I ! in feet i in acres ! acre -feet $$ 5 60 20 33 15 70 61 W*o 25 80 110 1,290 35 90 150 2 5 590 k$ 100 190 1**290 SS 110 230 6,390 65 120 270 8,890 75 130 300 11,700 85 11*0 3h0 ll*,900 95 150 380 18,500 105 160 U30 22,600 115 170 1*80 27*100 125 180 530 32,200 135 190 580 37,700 11*5 200 630 1*3 5 800 155 210 670 50,300 165 220 720 57,200 169 22 1* 71*0 60,100 175 230 770 61*, 700 185 2l*0 830 72,700 195 250 890 81,300 °222° A geologic investigation of the San Simeon dam site was made in 195>5> by geologists of the Division of Water Resources „ No prior geologic work at the site is known, nor has exploratory drilling of the foundation or borrow areas been done c Available information indicates that the site is suitable for construction of an earthfill dam up to a maximum height of about 200 feeto Rocks at the site consist of well consolidated sandstone , shale s and some chert and metamorphosed volcanics, all of which are a portion of the Franciscan series o Outcrops in the vicinity are scattered and indicate com- plex geologic structure which is typical of the Franciscan series „ All out- crops show jointing,, and shears are abundant in the softer rocks The rocks should take moderate to heavy grouting In the channel section, an estimated average depth of about I4.O feet of gravel and three feet of loose rock would be stripped under the impervious core of the dam Stripping on the left abutment is estimated to be about three feet of soil and ten feet of loose rock Stripping on the right abut- ment is estimated to be an average of 15 feet of loose rock with only about five feet necessary on the steep slope o For the pervious section,, a nominal depth of stripping of two feet was assumed throughout the contact area c A yield study was made for a reservoir storage capacity of 60 s 000 acre-feet at the San Simeon site c Results of that study , which are presented in Appendix K, show that a dam 175 feet high, impounding 60,000 acre-feet of water, would produce gross and net safe seasonal yields of 18 5 5>00 and 18,200 acre-feet, respectively <> The 300 acre-foot difference between the gross and net yield of the reservoir represents the probable ultimate mean seasonal water requirement of lands overlying San Simeon Basin not affected by con- struction of San Simeon Dam and Reservoir o The relationship between reservoir storage capacity and net safe seasonal yield for San Simeon -223=- Reservoir is shown on Plate 22. After consideration of results of yield studies and geologic recon- naissance, a detailed estimate of cost was prepared for an earthfill dam and reservoir having a storage capacity of 60,000 acre-feet, which estimate is presented in Appendix L. General features of the dam and reservoir are given in Table 1±Z<. -22k- 1 TABLE hi GENERAL FEATURES OF A DAM AND RESERVOIR AT THE SAN SIMEON SITE ON SAN SIMEON CREEK Characteristics of Site Drainage area^lH^^ square miles Estimated average seasonal runoff--2lj,l|00 acre-feet Estimated average net seasonal depth of evaporation— 8 53 feet Estimated sedimentation--500 acre-feet Elevation of stream bed., U°S<,GoS datum-^55 feet sGross reservoir storage capacity 5 % in acre-feet )0,000~ Earthfill Dam Crest elevation^, in feet, UoSoGoSc datum 237 Crest lengthy in feet 2,230 Crest widths in feet 30 Height, spillway lip above stream bed, in feet 169 Side slopes , upstream and downstream 2o5sl & 3:1 Freeboard, above spillway lip, in feet 13 Volume of fill, in cubic yards k, 211 , 700 Reservoir Surface area at spillway lip?, in acres 71*0 Net storage capacity at spillway lip 5 in acre-feet 59,500 Type of spillway Chute Spillway discharge capacity, in second-feet 6,900 Type of outlet 148-inch diameter steel pipe Estimated net safe seasonal yield 5 in acre-feet 18,200 Capital Costs Dam and reservoir $6, 311;, 000 Per acre-foot of storage 105 Per acre-foot of net safe yield 31*7 Annual Costs Dam and reservoir 30li,200 Per acre-foot of net safe yield 16 = 70 =225= Only one capacity of reservoir was studied for this site due to the fact that several sizes of dams and reservoirs were studied for the so- called Palmer Flats site about o 8 mile upstream<> These studies were abandoned due to the discovery of a large slide on the right abutment of the Palmer Flats siteo However , the studies established that smaller sizes of reservoirs on San Simeon Creek would give lower unit costs of reservoir yield, but that a development of about 60,000 acre-foot capacity would supply water at costs which are believed to be within the upper limit of economic feasi- bility in the area,, An earthfill structure was contemplated at the San Simeon site, comprising an impervious core of select earth material with upstream and downstream sections of semipervious random fill material „ The upstream face of the dam would be protected against wave action by rock riprap placed to a depth of three feet normal to the si ope Adequate impervious material is available within a mile of the site Alluvial gravels appear to be abundant in the channel and reservoir area for semipervious random fillo Material stripped from the foundation of the dam should be suitable for use as random fill Riprap would be selectively quarried from the volcanic rocks out- cropping near the site Employment of semipervious random fill in the outer sections would necessitate the installation of gravel blankets and drains at the downstream face of the impervious section as a precautionary measure to carry away possible leakage that might occur through the impervious section and at the abutment s» The spillway would have a discharge capacity of 6,900 second-feet, and was designed as a concrete-lined chute with an ogee weir control section. The spillway would be excavated through the left abutment around the end of the dam -226- The outlet works would be located on the left abutment s The intake structure would be a short concrete tower with a steel trash rack at its entrance A concrete pressure conduit would be installed beneath the dam and would extend from the intake to a gate chamber located slightly upstream from the axis of the dam» Within the gate chamber, an emergency high pressure slide gate would be installedo A reinforced concrete culvert, founded on bedrock^, would extend from the gate chamber to the valve house at the down- stream toe of the dam and would house an access passageway to the gate chamber as well as a U8-inch steel outlet pipe supported on cradles o Releases would be regulated by a Howell=Bunger valve and a needle valve located at the downstream end of the outlet pipe It was estimated that the dam would require an estimated two years for construction^, and, therefore, it was assumed that a closure section of the earthfill embankment to accommodate diversion of the stream during con- struction would be kept open the first year Q Construction of a dam at the San Simeon site would require the relocation of about k<>5 miles of county roado Several ranches and power and telephone lines are included in the reservoir area Santa Rosa Dam and Reservoir o The Santa Rosa dam site is located on Santa Rosa Creek about seven miles upstream from its mouth and in the south half of Section 16, Township 27 south, Range 9 east, M„ Do B» & M„ Consideration was given to the construction of a dam and a reservoir at the Santa Rosa site for storage of flood waters in Santa Rosa Creek and utiliza- tion of water so conserved in the Cambria and San Luis Obispo Subunits of the Coastal Hydrologic Unito =227= A topographic map of the Santa Rosa dam site at a scale of one inch equals 100 feet, with 10-foot contour intervals, was prepared in the field by the Division of Water Resources in 1955 o Reservoir areas and storage capacities for various heights of dams were computed from U» S. Geological Survey quadrangles at scales of ls2h 5 000 and ls62,500, with contour intervals of 20 feet and 50 feet, respectively^ and are presented in Table U8« .228- TABLE 1*8 AREAS AND CAPACITIES OF SANTA ROSA RESERVOIR Depth s Water surface Water : Storage of water § elevation ? s surface s capacity, t at dam j U0S0G0S0 datum 5 s area, ; in in feet t in feet : in acres : acre-feet 21*0 10 250 1 3 20 260 20 110 30 270 36 390 ho 280 55 8U0 50 290 71 1,U70 60 300 86 2,250 70 310 110 3,230 80 320 130 1*,1*30 90 330 150 5,830 100 3l*0 160 7,380 110 350 190 9,130 120 360 210 11,100 130 370 230 13,300 138 378 21*0 15,200 li*0 380 250 15,700 150 390 270 18,300 160 1*00 300 21,200 170 1*10 330 2U,300 172 U12 3ii0 25,000 180 1*20 370 27,800 190 1*30 1*00 31,700 198 1*38 1*20 35,000 200 kho 1*30 35,800 210 hSo 1*60 1*0,300 220 i*6o 1*90 l*5 5 ooo 230 1*70 520 50,100 21*0 1*80 550 55,1*00 250 1*90 580 61,100 260 500 620 67,1°° =229= „ Based upon preliminary geologic reconnaissance, the Santa Rosa dam site is considered suitable for an earthfill or concrete dam A geologic investigation of the Santa Rosa dam site was made in 195>U by geologists of the Division of Water Resources No prior geologic work at the site is known, nor have the foundation or borrow areas been explored by drilling,, Bedrock at the site consists of slightly altered basaltic rock and some agglomerate ? both of the Franciscan series <, The structure is unknown, but the volcanic rock underlies the ridge of the left abutment and extends well into the hill of the right abutment o The rocks are very highly fractured and faulted, and slickenside surfaces are found throughout the outcrops <> Along some of the fractures the rock has a cherty appearance, and along other fractures resembles serpentine <, Quartz veins up to two inches wide were i noted as well as a few calcite stringers „ In many places, the rock has been highly brecciatedo No open fractures were noted, and very little grout should be required unless open fractures are encountered at depth. In spite of the high degree of fracturing, the rock appears to be quite strong and should be adequate for an earthfill or concrete dam The left abutment consists of a long narrow ridge which may pass an excessive amount of seepage and may, therefore, require blanketing with impervious material In the channel section, it is estimated that a depth of about 20 feet of fractured rock would have to be stripped under the impervious section of an earthfill dam Stripping on the right abutment beneath the impervious section would probably include five feet of soil and about 15 feet of loose and overhanging rock On the left abutments, stripping is estimated to con- sist of one foot of soil and eight feet of loose rock For the random fill sections of the dam, a nominal depth of stripping of two feet may be required throughout the contact area a 230- o Yield studies were made for reservoir storage capacities of 15,000, 25 5 000, and 35,000 acre-feet at the Santa Rosa site and are summarized in Appendix K The estimates of safe seasonal yield obtained from these studies were as follows? Gross reservoir Safe seasonal Height storage yield, of dam, capacity, in acre -feet in feet in acre-feet Gross : Net 138 1^,000 7,900 7,300 172 25,000 7,800 9,200 198 35,000 11,700 11,100 The 600 acre-foot difference between the gross and net reservoir yields presented in the foregoing tabulation, represents the probable ultimate mean seasonal water requirement of lands overlying Santa Rosa Basin not affected by construction of Santa Rosa Dam and Reservoir,, The relationship between reservoir storage capacity and net safe seasonal yield for Santa Rosa Reservoir is shown graphically on Plate 22 After consideration of the results of yield studies, geologic reconnaissance, and topography of the site, detailed estimates of cost were prepared for an earthfill dam and reservoir of each of the foregoing three sizes, which estimates are presented in Appendix L a General features of the three sizes of dam and reservoir are listed in Table U9« 231= TABLE U9 GENERAL FEATURES OF THREE SIZES OF DAM AND RESERVOIR AT THE SANTA ROSA SITE ON SANTA ROSA CREEK Characteristics of Site Drainage area— 114*9 square miles Estimated average seasonal runoff~»l6,200 acre-feet Estimated average net seasonal depth of evaporation—lo 83 feet Estimated sedimentation~-500 acre-feet Elevation of stream bed, U.S.GoS. datum--2li0 feet sGross reservoir storage capacity, : in acre-feet t 15,000 i 25,000 s 35,000 Earthfill Dam Crest elevation, in feet, UoSoGoSo datum 393 12$ U50 Crest length, in feet 570 800 965 Crest width, in feet 30 30 30 Height, spillway lip above stream bed, in feet 138 172 198 Side slopes, upstream and downstream 25sl 3*1 3*1 Freeboard, above spillway lip, in feet 15 13 12 Volume of fill, in cubic yards 658,800 1,378,100 2,08l,U00 Reservoir Surface area at spillway lip, in acres 250 3U0 1*30 Net storage capacity at spillway lip, in acre-feet il4,5oo 2)4,500 3*4,500 Type of spillway Side channel with concrete- lined chute Spillway discharge capacity, in second-feet 7,1*00 6,900 3,800 Type of outlet 30-inch 36- inch 142-inch diameter diameter diameter steel steel steel pipe pipe pipe Estimated net safe seasonal yield, in acre-feet 7,300 9,200 11,100 Capital Costs Dam and reservoir $2,068,000 $3,080,000 H4, 121, 000 Per acre-foot of storage 138 123 118 Per acre -foot of net safe yield 283 335 371 Annual Costs Dam and reservoir $101,900 $1149,200 $198,800 Per acre-foot of net safe yield 111 « 00 16, 20 17*90 Per acre-foot of incremental net safe yield -»— 214*90 26d0 -232- For all heights of dams an earthfill structure was contemplated,, comprising an impervious core of select earth material with upstream and downstream sections of semipervious random fill material Employment of semipervious random fill in the outer sections would necessitate the installation of a gravel blanket and drains as a precautionary measure to carry away possible leakage that might occur through the impervious section and at the abutments o The upstream face of the dam would be pro- tected against wave action by rock riprap placed to a depth of three feet normal to the slope a Areas of impervious material occurring in the reservoir area are not large o There may be about 200,000 cubic yards of impervious material on the valley floor , on terraces , and on hillsides in the reservoir area within two miles of the dam site<> Additional impervious fill could be obtained from the flats downstream from the site<> Part of this land would necessarily have to be acquired because it may be adversely affected by spillway dis- charge,, Bedrock and possibly stream deposits are available for random fill locally Satisfactory riprap was not noted in the immediate vicinity of the site, but suitable rock could be selectively quarried from the volcanic rock outcrops in the reservoir area The spillway was designed as a concrete-lined chute with ogee weir control sections and would have a discharge capacity of about 3,800 second- feeto The spillway would be excavated through a saddle on the left abutment and discharge into Santa Rosa Creek about 1,000 feet downstream from the toe of the dam The intake structure for the outlet works would be located on the left abutment,, This structure would be a short concrete tower with a steel trash rack at its entrance „ A concrete pressure conduit would be installed -233- beneath the dam and would extend from the intake to a gate chamber located slightly upstream from the axis of the dam. Within the gate chamber s an emergency high pressure slide gate would be installed,, A reinforced con- crete culvert would extend from the gate chamber to the valve house at the downstream toe of the dam. This culvert would house an access passageway to the gate chamber as well as a steel outlet pipe supported on cradleso The outlet pipe would have a diameter of \\2 inches 3 and releases would be regulated by a combination of a Howell-Bunger and needle valve <, It was estimated that the dam could be constructed within one year and summer flow of Santa Rosa Creek could be diverted through the outlet conduit. However , the total construction time was estimated to be two years due to the required relocation of about 3«7 miles of State Highway 1*1 <> The first year of construction could be devoted to relocation of the state highway and spillway construction,. Five fairly large ranches are located in the reservoir area and another lies just downstream from the dam and spillway sites. Several local power and telephone lines are also located in the reservoir area. Estimated costs of acquisition of lands required for the reservoir do not include a cost for the mineral rights at Oceanic Mine which would be inundated by the reservoir because the mine appeared to be abandoned. Whale Rock Dam and Reservoir The Whale Rock dam site is located on Old Creek in the Morro y Cayucos land grant,, approximately 1,1 miles upstream from the mouth of the stream and about one-half mile east of Cayucos, Consideration was given to construction of a dam and reservoir at the Whale Rock site for storage of surplus waters of Old Creek 5 and utilization of the waters so conserved in the Cambria and San Luis Obispo Subunits of the Coastal Hydrologic Unit, -23U- The Whale Rock reservoir area was mapped by photo grammetric methods at a scale of one inch equals 500 feet, with a contour interval of 25 feet s by the Division of Water Resources in 1955» The dam site was mapped from similar data at a similar scale but with contour interval of 20 feeto Reser- voir areas and storage capacities computed from the reservoir map are presented in Table $Q a =235- TABLE 50 AREAS AND CAPACITIES OF WHALE ROCK RESERVOIR Depth : Water surface s Water : Storage of water ! elevation, s surface s capacity, at dam, : s U »S oG <,S datum, s area. s in in feet 1 l in feet J in acres 2 acre-feet 1*0 10 50 1 3 20 60 10 58 30 70 20 210 ko 80 50 560 50 90 90 1,260 60 100 130 2,360 70 110 180 3,910 80 120 220 5 S 910 90 130 260 8,310 100 mo 310 11,200 110 150 360 iU,5oo 120 160 ilOO 18,300- 12i| I6J4 U20 20,000 130 170 kSo 22,600 lho 180 500 27,300 150 190 550 32,500 160 200 600 38,200 163 203 610 Uo,ooo 170 210 650 10i,ii00 180 220 690 51,100 190 230 750 58,300 200 2I4O 810 66,100 210 250 900 7^,600 -236= o Based upon preliminary geologic reconnaissance, the Whale Rock site is considered suitable for an earthfill dam of moderate height « Geology of the site was investigated by the Division of Water Resources in 19S>l|o No exploratory drilling or trenching of the foundation has been done at this site« Results of tests conducted on a single sample of the borrow material indicate the borrow material has relatively low shear strength and density., Further detailed exploration and testing of the foundation and borrow areas would be required in order to adequately determine necessary design precautions Bedrock at the site consists of slightly metamorphose basaltic rock of the Franciscan series o Serpentine is exposed on the right abutment about 200 feet above the stream bed and near the downstream toe of the proposed dam s The serpentine-basalt contact dips about 30 degrees downstream „ However s the main portion of either of the two heights of dam considered would abut the basaltic rock Q If higher dams were to be considered^, excess leakage may occur at the contacto The basalt is soft 5 highly weathered^, and appears to be highly fractured. The fractures seem tight 9 however , and it is likely that only moderate grouting will be required^, except at larger fracture zones and in the serpentine In the channel section of the dam,, it was estimated that a depth of 30 feet of gravel and three feet of loose bedrock would have to be stripped under the impervious core On the left and right abutments 9 it was further estimated that about three feet of soil and seven feet of loose rock would have to be removed for the impervious section,. For the random fill sections 9 a nominal depth of stripping of two feet may be required throughout the contact area Yield studies were made for reservoir storage capacities of 20^,000 and UO^OOO acre-feet at the Whale Rock site and are summarized in Appendix K -237= The estimates of safe seasonal yield obtained from these studies were as follows s Gross reservoir Safe seasonal Height storage yield, of dam, capacity, in acre-feet in feet in acre -feet Gross s Net 121a 20,000 6,600 6,300 163 1*0,000 9,200 8,900 The difference between gross and net yields presented in the fore- going tabulation, in the amount of 300 acre-feet, represents the sum of estimated present exports from lower Old Basin and probable ultimate mean seasonal water requirements of lands overlying Old Basin which would not be affected by construction of Whale Rock Dam and Reservoir . The relationship between reservoir storage capacity and net safe seasonal yield for Whale Rock Reservoir is shown graphically on Plate 22 «, After consideration of results of the yield studies, preliminary geologic reconnaissance, and topography of the site, detailed estimates of cost were prepared for earthfill dams and reservoirs having storage capacities of 20,000 and U0,000 acre-feet, which estimates are presented in Appendix L. General features of the two sizes of dam and reservoir are listed in Table £1. =238- TABLE 5l GENERAL FEATURES OF TWO SIZES OF DAM AND RESERVOIR AT THE WHALE ROCK SITE ON OLD CREEK Characteristics of Site Drainage area>=»20o3 square miles Estimated average seasonal runoff—13,320 acre-feet Estimated average net seasonal depth of evaporation- 2.96 feet Estimated sedimentation^ -=500 acre-feet Elevation of stream bed, U,S,G So datum~<4iQ feet sGross reservoir storage capacity, s in acre-feet 20,000 % kO s QQO Earthfill Dam Crest elevation, in feet, ULSoGoSo datum 177 215 Crest length., in feet 575 720 Crest width., in feet 30 30 Height 3 spillway lip above stream bed, in feet 12U 163 Side slopes, upstream and downstream 2.5*1 2o5?l Freeboard, above spillway lip., in feet 13 12 Volume of fill, in cubic yards 630,300 1,313,200 Reservoir Surface area at spillway lip, in acres 1x20 620 Net storage capacity at spillway lip, in acre-feet 19,500 39,500 Type of spillway Side channel with concrete-lined chute Spillway discharge capacity, in second-feet 8,600 7,100 Type of outlet 30-inch i;2-inch diameter diameter steel steel pipe Pipe Estimated net safe seasonal yield, in acre-feet 6,300 8,900 Capital Costs Dam and reservoir .,9^3,000 $2, 881*, 000 Per acre-foot of storage 97 72 Per acre-foot of net safe yield 308 321* Annual Costs Dam and reservoir 96,000 llil,600 Per acre-foot of net safe yield I5o20 I5o90 Per acre-foot of incremental net safe yield 17„50 >239- The iiO^OOO acre-foot reservoir would require an earthfill dam com- prising an impervious core of select earth material , and upstream and down- stream sections of seraipervious random fill material. Based on preliminary reconnaissance , it is estimated that ample earthfill material, suitable for the impervious section of the dam, occurs within two miles upstream of the site Random fill material could probably be obtained from the reservoir area and salvage of excavated materials Employment of semipervious random fill in the outer sections would necessitate installation of a gravel blanket and drains along the downstream face of the impervious section to carry away any water seeping through the impervious core© The upstream face of the dam would be protected against wave action by rock riprap placed to a depth of three feet normal to the slope. Riprap rock could be imported from a source outside the reservoir area or salvaged from the spillway excavation. The concrete-lined spillway for the dam would be located on the left abutment and was designed as a chute type with a side-channel control section,, The spillway would have a discharge capacity of 7,100 second-feet and would discharge into Old Creek about 150 feet downstream from the toe of the dam„ The alternative spillway location was considered through a saddle located about one mile east of the dam site and which would spill into Willow Creek<, Although the spillway structure at this location would be cheaper than on the left abutment, the costs of acquiring necessary rights of way and replacement of existing bridges along Willow Creek were estimated on a preliminary basis to be greater than the savings in cost of the structure,, However, the possibility of utilizing this saddle should be explored further if design of a dam is undertaken at this site. =2li0* . The outlet works for the dam would have a concrete intake structure at the upstream toe near the right abutment, with a steel trash rack at its entrance o A concrete pressure conduit beneath the dam would extend from the intake to a gate chamber located slightly upstream from the axis of the dam, wherein a high pressure slide gate would be installed e A reinforced-concrete culvert, founded on bedrock, would extend beneath the dam from the gate chamber to the valve house, and would contain an access passageway to the gate chamber as well as a steel outlet pipe supported on cradle s<> The outlet pipe would have a diameter of 42 inches <, It was estimated that the dam could be con^ structed within one year, and that summer flow of Old Creek could be diverted through the outlet conduit during construction Included in the reservoir area are four partially irrigated ranches, a recently installed substation of Pacific Gas and Electric Company, a power transmission line, a telephone line, and a county road„ The cost of these lands and improvements and relocations form a substantial portion of the total cost of the project „ The length of required road relocation and im- provement would be 3°9 miles Subsequent to the preparation of the original cost estimate for the Whale Rock Dam and Reservoir in 1954 > a service agreement was executed in the fall of 1956 between the Department of Water Resources, and the Division of Architecture, providing for further investigation of Whale Rock Project as a possible source of supplemental water for California State Polytechnic College and the California Men's Colony . It was anticipated that construction of the Whale Rock Project might be undertaken by the two foregoing State agencies as a joint venture with the City of San Luis Obispo -210.- Work tinder the agreement involved additional exploration of the foundation and borrow areas and the preparation of a revised cost estimate of the Whale Rock Project, including costs of the .dam, reservoir, and conveyance conduit from the dam to the proposed service area. The additional explora- tion work 'included the drilling of three diamond drill holes along the axis of the dam and a number of holes in proposed borrow areas. Strength and com- paction test were conducted on samples obtained from the drill holes. Results of the foregoing additional exploration work indicate that the cost of the Whale Rock Dam and Reservoir would be greater than that shown in Table 5?Lo Factors which indicate this greater cost include: (l) diamond drilling logs demonstrate the need for about 50 per cent more stripping in the channel section and on both abutments than was originally- contemplated, (2) tests of borrow material showed it to have low strength necessitating the use of flatter slopes for the dam section than were originally assumed, resulting in the need for a substantially greater amount of embankment material in the dam cross-section , and (3) the value of lands in the reservoir area has increased rapidly during recent years. It is not considered that the conclusion as to the desirability of construction of the Whale Rock ,Project would be affected by the indicated increase in cost. Lopez Dam and Reservoir . The Lopez dam site is located on Arroyo Grande Creek about 0.2 of a mile below the confluence with Lopez Creek and on the line between Sections 32 and 33? Township 31 south, Range 14 east, M. D. B. & M. Consideration was given to construction of a dam and reservoir at the Lopez site for control of floods on Arroyo Grande Creek and utiliza- tion of the flood waters conserved in the Arroyo Grande Subunit of the Coastal Unit. -242 » The Lopez dam site was mapped up to an elevation of 550 feet in 1946 by the U, S„ Bureau of Reclamation at a scale of one inch equals 50 feet ? with a five-foot contour interval „ The reservoir area was mapped by the Bureau in 1947 to an elevation of 500 feet at a scale of one inch equals 500 feet with 10- foot contour intervals This was supplemented by interpola- tion up to an elevation of 550 feet from a U 3 So Geological Survey quadrangle, at a scale of Is 62 , 500 and with a contour interval of 50 feeto Reservoir areas and storage capacities at various stages of water surface elevation, computed from the foregoing maps, are given in Table 52 =343- TABLE 52 AREAS AND CAPACITIES OF LOPEZ RESERVOIR Depth s Water surface • Water : Storage of water : elevati on, e surface : capacity, « at dam, : D » S oG °S o datum, area, ! in o in feet : in feet o in acres l acre-feet 375 5 380 2 5 15 390 Hi 85 25 Uoo 53 it 20 35 iilO 100 1,190 U5 U20 160 2,1490 55 1*30 21*0 U,li90 65 hho 280 7,090 75 U50 330 10,100 85 U6C 380 13,700 95 U70 kho 17,800 105 1*80 520 22,600 110 U85 570 25,000 115 U90 620 28,300 125 500 730 35,ooo 135 5io 8U0 1*2,800 1U3 518 9k0 50,000 11*5 520 960 51,800 155 530 1,090 62,100 165 5Uo 1,230 73,700 175 550 1,370 86,700 -2UU- A geologic investigation of the Lopez dam site was made in 1954 by- geologists of the Division of Water Resources . The geology of this site had been previously mapped and reported upon by the U Q S Bureau of Reclamations but no exploratory drilling or trenching of the foundation has been done. Based upon preliminary geologic reconnaissance, Lopez dam site is considered to be suitable for a moderate to large sized earthfill dam with the spillway on the right abutment,, Geology of the bedrock is rather complex and outcrops are poor except in the road cuts on the left abutment „ The region for about 1,000 to 1,500 feet both upstream and downstream from the axis appears to be part of a fault sliver with the Franciscan formation to the west and the Monterey formation to the easto The intrusive member of the bedrock at the site was called gabbro by U S Bureau of Reclamation geologists. In the road cut on the left abutment , rock types include interbedded tuffaceous or rhyolitic rocks, volcanic breccias, and some shales and siltstones, all intruded by gabbroic or basaltic rocksb The gabbroic intrusives vary in width from two feet to 30 feet and generally dip upstream „ All of these rocks are highly fractured and would require heavy grouting Exposures on the right abutment are poor, but the bedrock is about the same as that described above The bedrock generally is strongo The rhyolitic and tuffaceous materials are of low density and should be tested for strength and density before being salvaged for use as fillo All rocks are weathered on the outcrop but the intrusive rock is generally the least weatheredo Stripping on both abutments under the impervious section of the dam would include an estimated five feet of soil and 15 feet of loose rock. Stripping the channel section would require removal of an estimated average of 50 feet of gravel with a probable maximum of 100 feet. =245° Yield studies were made for reservoir storage capacities of 25,000 and 50,000 acre-feet at the Lopez site. These studies are summarized in Appendix K. Estimates of safe seasonal yield obtained from these studies were as follows: Gross reservoir Safe seasonal Height storage . yield, of dam, capacity, in acre-feet in feet in acre-feet Gross ; Net 110 25,000 9 S 800 3,800 L43 50,000 12,500 6,500 As discussed in Chapter II y it was estimated that an additional 3,000 acre-feet of water over and above the present net draft could be obtained from Arroyo Grande Basin without violation of any of the previously stated criteria for safe yield. It was further estimated that, with construction of a dam at the Lopez site, approximately 3,000 acre-feet of water per season would have to be released in order to maintain historical ground water levels. The estimated safe seasonal gross yield of Lopez Reservoir was, therefore, reduced by the sum of the two foregoing values, or 6,000 acre-feet, to obtain » the estimated value for new water. The relationship between reservoir storage capacity and net safe seasonal yield for Lopez Reservoir is shown on Plate 22. After consideration of results of the yield studies, geologic reconnaissance and the topography of the site, detailed estimates of cost were prepared for earthfill dams at the Lopez site creating reservoir storage capacities of 25,000 and 50,000 acre-feet, respectively. Detailed cost estimates of two sizes of dam and reservoir at the Lopez site are presented in Appendix L. General features of the two fore- going sizes of dam and reservoir are listed in Table 53 <> -246- TABLE 53 GENERAL FEATURES OF TWO SIZES OF DM AND RESERVOIR AT THE LOPEZ SITE ON ARROYO GRANDE CREEK Characteristics of Site Drainage area- ,1 square miles Estimated average seasonal runoff—18,300 acre-feet Estimated average net seasonal depth of evaporation- 2.U0 feet Estimated sedimentation-~l,000 acre-feet Elevation of stream bed, U.S.GoSo datum—375 feet iGross reservoir storage capacity, ; in acre-feet 25,000 o 50,000 Earthfill Dam Crest elevation, in feet, U0S0G0S0 datum 505 531* Crest length, in feet 861* 98U Crest width, in feet 30 30 Height, spillway lip above stream bed 5 in feet 110 11*3 Side si opes s upstream and downstream 2 5sl 2o5§l Freeboard, above spillway lip, in feet 20 16 Volume of fill, in cubic yards 1,169,800 1,828,1*00 Reservoir Surface area at spillway lip, in acres 570 91*0 Net storage capacity at spillway lip 5 in acre-feet 21*, 000 k9 $ O00 Type of spillway Ogee weir with concrete-lined chute Spillway discharge capacity, in second-feet 17,700 13,800 Type of outlet 36-inch U8-inch diameter diameter steel steel pipe pipe Estimated net safe seasonal yields in acre-feet 3,800 6,500 Capital Costs Dam and reservoir $3,070,000 III, 228,000 Per acre-foot of storage 123 85 Per acre-foot of net safe yield 808 650 Annual Costs Dam and reservoir 1U8,700 205,500 Per acre-foot of net safe yield 39olO 31 060 Per acre-foot of incremental net safe yield 21c00 °2U7= „ „ For all heights of dam a rolled fill structure was contemplated comprising an impervious core of select earth material and upstream and down- stream sections of semipenrious random fill material. Employment of semi- pervious random fill in the outer sections would necessitate the installation of gravel blankets and drains at the downstream face of the impervious section as a precautionary measure to carry away possible leakage that might occur through the impervious section and at the abutment s» The upstream face of the dam would be protected against wave action by rock riprap placed to a depth of three feet normal to the slope There are an estimated 1 ? 000^000 cubic yards of impervious material in the reservoir area within two miles of the site c The stream gravels appear suitable for use as random fill 5 but they should be thoroughly tested for strength and iiensity The Division of Water Resources tested a sample of the proposed impervious borrow material and classified it as a silty sand A maximum density of 104 pounds per cubic fo,ot was obtained in the compaction test of this nonplastic materialo Results of this test? though of a prelim- inary nature,, were incorporated into designs adopted for cost estimating purposes „ Riprap may be selectively quarried near the site from the gabbroic intrusives The spillway would have a discharge capacity of 13^800 second-feeto The spillway was designed as a concrete-lined chute with an ogee weir control section and would be located on the right abutment The outlet works 'would consist of a concrete intake structure located at the upstream toe of the dam near the left abutment with a steel trash rack at its entrance „ A concrete pressure conduit beneath the dam would extend from the intake to a gate chamber located slightly upstream from the axis of the dam wherein a high pressure slide gate would be -24S- „ „ . installedc A reinforced concrete culvert, founded on bedrock, would extend beneath the dam from the gate chamber to the valve house at the downstream toe of the damo This culvert would house an access passageway to the gate chamber as well as a steel outlet pipe supported on cradles „ The outlet pipe would have a diameter of IS inches „ Releases would be regulated by a Howell~ Bunger valve and a needle valve located in the valve house It was estimated that the dam could be constructed within one year and summer flow of Arroyo Grande Creek could be diverted through the outlet conduit during construction Construction of a dam at the Lopez site would require the relocation of about 13 ol miles of county roads „ Improvements in the reservoir area include a one-room school house , a county park, a small gravel plant, a private camp ground, seven ranches including some irrigated and nonirrigated farm land, and telephone and power lines Alternative Plans for Water Supply Development This section contains a discussion of the various possible alter- native plans for water supply development in San Luis Obispo County, with particular regard to their relative capability of meeting future supplemental water requirements of various parts of the County „ Eoonomic factors pertinent to the selection of feasible water projects for eventual future construction are discussed as are some organizational and financial aspects involved in water resources developement in San Luis Obispo County The selection of a plan for the development of the water resources of San Luis Obispo County and subdivisions thereof, was based on consider- tion of the following principal factors; (l) present and estimated future supplemental water requirements of potential service areas, (2) the net safe -249- seasonal yield or amount of new water that would be developed by a particular project compared to that which would be developed by an alternative project,? (3) the capital cost of a given project compared to that of alternative projects, (A) the annual cost of net safe yield that would be developed by a given project compared to that by alternative projects, (5) the annual cost of incremental net safe yield that would be developed from various sizes of structures comprising a given project , and (6) the estimated cost of imported water. Possible plans for the importation of water, which are discussed subsequently, could made a considerable amount of supplemental water avail- able to San Luis Obispo County* Although it should not be considered as substitute for supplies available from potential local conservation works, the estimated cost of imported water delivered into the County from outside sources was used in this bulletin as a general guide in establishing the upper limit of practicable development of the local water resources of San Luis Obispo o In selecting the capacities of reservoirs hereinafter recommended for incorporation into the overall plan of development, where no physical limitations of the sites were apparant, the sizes of surface storage develop- ments were increased to the point where the incremental costs of new water yields produced thereby would be generally equivalent to the estimated cost of imported water. It was found that this procedure would, while having a reasonably sound economic basis, result in a relatively high degree of con- servation of surface runoff and leave only some very infrequent flood flows to waste to the ocean, It is hereinafter estimated that imported water from northern California could be delivered to the Upper Salinas Unit in Cholame Creek o at a cost of from $20 to $30 per acre-feet, depending on the amount 250= o „ served and based upon certain assumptions as described later,, Approximate cost of conveyance of this water to strategic locations in San Luis Obispo County were given consideration in the foregoing comparison of cost of un- imported water with incremental costs of local storage and conveyance develop- ment S o It is recognized that several of the water supply developments discussed previously will require relatively large capital expenditures for construction The question of whether they will ever be built, or the prder in which they will be built , will be a matter for local decision „ Major factors affecting that decision will be the extent of need for supplemental water, the availability of an imported supply, and the unit cost thereof as compared to the unit cost of yield which could be obtained from a local water supply development » Construction of the more expensive local develop- ments will therefore probably be deferred if increasing demands for supplemental water do not force their construction prior to the arrival of imported water supplies in San Luis Obispo County For comparative purposes, there is presented in Table 54 a recapitu- lation of yields of water that could be developed by construction of the several storage capacities considered at each of the eleven dam and reservoir sites given detailed study in San Luis Obispo County . Presented also in Table 54 are comparisons of certain economic factors pertaining to each reservoir Unit costs of water presented are indicative of such costs at the reservoirs and do not include costs of conveyance or distribution » Graphical interpretations of certain data presented in Table 54 are shown on Plates 21, 22, and 23 ° Discussions of various water supply plans are presented in the following paragraphs =251= . © i 3» TJ o ( © 1 o o 8 fa a • 5k CO 9 SO !§s°- 8 *» «4 • o o « 1 e o I tN. 6 ON 3 HJ.* o o en 3 CM HI HJ CN faSSS « m (fa %• H) *» 1 • o o Q O o o o o o O o o OOP o • • K 1 ^- HI © as ON CM ONSO © O SO © aoao H CN cpfiap usj- CM H! HI o irs^s. CN cs C\ CN CN. «M CS Un o © at •t » It, C' a. c O SB • 4?" © © B0 *» UNCN0O O PA CM CM HI C^» H CM O UN 4-c *o 4 O 0O f»v CSCM MNUNj. 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O o s o o o O O o o o o o o O O o o l« onco r^ NO CM CO UN +> ft ft c NO ON 4 t/5 ft • > • o o o O O o o n tc +> • o o o o o o o » 1 -H «-l o o o o o o o p b a C i ft ft ft ft ft ft ft b o «j -* • UN UN UN o o UNO O +J Q. b iH CM ON CMJ* CM UN OT * © 5 © tt T3 C o •o o • 3 C P•rt c s o a o u 4 O — o * to &-• 4 o u fr» c «> tH to OS « o a » PS o u M J ri c o •< +J 3 to ol s 53o to o 253- Based on criteria discussed previously in this chapter, it is indicated that, construction of a reservoir oh Jack Creek at the Lower Jack site offers one of the cheapest sources of supplemental water in the Upper Salinas Unit, in terms of unit cost. The average annual cost per acre-foot of net safe seasonal yield from Lower Jack Reservoir is estimated to be $18.90 for the 25,000 acre-foot storage capacity. This is somewhat less expensive than the yield of the smaller reservoir considered at the same site. Larger sizes were not considered since a reservoir with a storage capacity of 25,000 acre-feet would develop about 70 per cent of the estimated runoff of Jack Creek and incremental costs of new yield were found to be very near to the costs of imported water. Water from this reservoir could be conveyed by conduit to nearby areas of use, or it could be released to the natural stream channel for percolation into the downstream ground water basin, from which it could be pumped by wells. Lower Jack Reservoir appears to be one of the most desirable local developments from which supplemental Water could be made available to the Paso Robles=Atascadero area and its relatively low capital cost would make the project attractive for construction by a local entity It was found that a 15,000 acre-feet dam and reservoir at the Santa Rita site on Santa Rita Creek would produce a net safe seasonal yield of about 3,200 acre-feet with an average annual unit cost per acre-foot of yield of about $22 o This cost per acre- foot of yield is nearly as low as Lower Ja&k site just described, and is also competitive with the cost of water imported from the Feather River Project. Of the local water supply developments for the Upper Salinas Unit shown in Table 54 s the Santa Rita development had the lowest estimated capital cost. A 15,000 acre-foot reservoir at the Santa Rita site could be constructed at a capital cost of about $1,400,000. Larger -254" o Sizes were not considered since their average annual cost per acre-foot of incremental net safe yield would increase substantially beyond the assumed unit cost of imported water „ It is therefore concluded that the Santa Rita Dam and Reservoir should be given consideration in future plans for water develop- ment in the Upper Salinas Unito Water service could be provided to the Paso Robles-Atascadero area in a manner similar to that proposed for operation of the Lower Jack development Nacimiento Pro.jects Results of detailed studies on the Nacimiento River above the existing Nacimiento Reservoir indicate that the San Miguelito and Jarrett Shut-in sites are feasible for the development of a water supply for the northern portion of the Upper Salinas Unito Of the two reservoir storage capacities studied at the San Miguelito site, the 130 5 000 acre-foot capacity appeared to be the most favorable for eventual construction „ Construction of a 130,000 acre-foot reservoir at the San Miguelito site as a secondary development to Nacimiento Reservoir would produce 13,000 acre-feet per season of new water at a cost per acre-fo6t of about $12, Three storage capacities were studied at the Jarrett Shut-In site,, The largest reservoir capacity of 110,000 acre-feet would probably be the most desirable, in view of the indicated need for maximum development of the storage potential at this site, and the estimated relatively low cost of the new water developedo Because of the structural requirements at the main axis, and the scarcity of materials for construction of a larger auxiliary dam, larger reservoir storage capacities were not studied. Results of studies of San Miguelito and Jarrett Shut-In Reservoirs, » . operated ©oordinately with Nacimiento Reservoir, show that the two reservoirs would yield 2li 5 100 aere=feet of new water per seasono The total capital coat ©f the two upstream projects would be $7,708,,QOOo The two developments would provide nawwater at a unit cost of $0L6olQ per acre=foot« The yields developed by the San Miguelito and Jarre tt Shut°In Reservoirs could be conveyed to potential service areas in the Upper Salinas Unit by a conduit system such as the Nacimiento-Shandon Conduit and Creston Lateral, shown on Plate llio Under the proposed plan, the foregoing yields would be released down the Naclmiento River , passed through the Nacimiento Reservoir , and diverted from the river into the Naciraiento=Shandon Conduit The Nacimiento°Shandon Conduit would take water from the Nacimiento River immediately downstream from Nacimiento Dam at an elevation of about 920 feeto The water would be pumped into a pressure conduit which would extend easterly from the dam and would divide at a bifurcation structure southeast of San Miguel o The main conduit would continue easterly therefrom to Shandon terminal reservoir, located about one mile southeast of the town of Shandon*, This portion of the conduit would include two booster pumping plants in addition to the one located at Nacimiento Dam. The Creston Lateral would extend in a general southeasterly direction from the bifurcation structure and would terminate in the Creston terminal reservoir about one mile south of Creston This lateral would also include two booster pumping plants „ The over-all length of the Naciraiento-Shandon Conduit would be about 31 miles Based exclusively on reconnaissance data, it was estimated that the combined Nacimiento=Shandon Conduit and Creston Lateral could be constructed at a capital cost of $6,i*62,OOQ and would convey the yields of San Miguelito and Jarrett Shut-In Reservoirs to the Creston-Shandon area at a total average annual cost, including costs of the two storage reservoirs, of about $38 per -256- . 'e-foot. The indicated cost of water exceeds the costs which farmers are terally encountering in developing local ground water resources in the upper .inas Unit under present conditions. As in the case of all local water ply developments, the timing of need for supplemental water and availability an imported supply, together with the financial capacity of the area served, .1, to a large degree, determine which units of a conveyance system such as i foregoing would ever be constructed, and the order of that construction ,stal Projects Two sites on San Carpoforo Creek were given detailed study, includ- . ; the Upper Ragged Point and the Bald Top sites One size of reservoir was .died at each site. Although hydrologic studies indicated that more yield Id be developed at each of the sites considered, the scarcity of construction erials precluded the consideration of larger dams than those studied. More ailed investigation of available materials of construction may result in .struction of larger developments at these sites. Coordinated operation studies indicated that storage capacities of 000 and 30>000 acre -feet at the Bald Top and Upper Ragged Point sites, peetively, would develop a combined net safe seasonal yield of 22,500 acre- 1 at a total capital cost of $7*669.? 000, ^nd. an average annual unit cost of i.50 per acre -foot. Comparative studies indicated that the Bald Top site, as rimary development, would be the cheaper of the two sites with regard to h capital cost and unit cost per acre -foot of yield. The two developments Id serve supplemental water to the coastal area north of San Simeon, as .1 as potentially water deficient areas to the south, through suitable veyance facilities hereinafter described. Results of water development studies indicate that the Yellow Hill -257= site on Arroyo de la Cruz is one of the most promising undeveloped sites in the County o Three reservoir capacities were studied at the Yellow Hill site Plate 21 illustrates that, within the range of capacities studied, the capital cost of Yellow Hill Reservoir varies uniformly with reservoir capacity „ It can also be seen from Plates 22 and 23 that the Yellow Hill Reservoir produces the greatest yield per acre=foot of storage capacity at the least unit cost for all reservoirs studied e An 80^000 acre-foot reservoir would produce a net safe seasonal yield of 27*300 at a unit cost of $11<,U0 per acre-foot, Studies indicated that reservoirs with storage capacities exceeding 80 s 000 acre-feet would have incremental unit costs in excess of the estimated unit cost of delivery of imported water to San Luis Obispo County,, For the foregoing reason* and because of the scarcity of embankment construction materials within reasonable haul distances, larger capacities were not considered at this site,, Yellow Hill Reservoir could provide water service to lands in the vicinity of San Simeon and could also be connected to conveyance facilities providing water service to the San Luis Obispo Subunito The San Simeon site is considered to be the most feasible of four sites studied on San Simeon Creek* Only a 60^000 acre-foot capacity reservoir was considered at the San Simeon site as prior studies at the Palmer Flats site, which was subsequently discarded because of poor geologic conditions, indicated that the 60,000 acre-foot capacity would supply water at costs which are believed to be within the upper limit of economic feasibility for the area,, A larger capacity at the San Simeon site was not planned since the foregoing capacity would control approximately 70 per cent of the runoff of San Simeon Creek o A reservoir constructed at the San Simeon site could provide water service to the San Simeon-Cambria area and could also be connected to a convey- ance system providing a supplemental water supply to the San Luis Obispo Subunit o o Reservoirs of three capacities, including one of 35*000 acre-foot capacity, were studied at the Santa Rosa site on Santa Rosa Creek Topographic limitations of the site and the fact that this capacity would control in excess of 70 per cent of the runoff of Santa Rosa Creek precluded the study of larger capacities,, Santa Rosa Reservoir could provide supplemental water to irrigated and urban lands in the Cambria-Cayucos area and could also provide water service to potentially water deficient areas in the San Luis Obispo Subunit to the south The Whale Rock Dam and Reservoir is considered to be the most feasible water supply development on Old Creek . Studies indicated that a 1*0,000 acre-foot reservoir at the Whale Rock site would yield about 8,900 acre- feet of new water per season. Preliminary cost estimates based on reconnais- sance surveys indicated that such a development would have a capital cost of about $2,8814,000 and deliver water at the dam at a unit cost of slightly less than $16 per acre-foot Larger capacities were not studied because of a reservoir of 1*0,000 acre-feet capacity would control in excess of 70 per cent of the mean annual runoff of Old Creek. Recent revision of the capital cost of this project previously referred to does not indicate the need for revision of the foregoing selected size of reservoir o Supplemental water could be furnished to the San Luis Obispo Subunit from Whale Rock Reservoir. Details of such a plan are presented in a subsequent section designated "Whale Rock Project" The Lopez site of Arroyo Grande Creek is considered the most economical for development of the several sites studied in the Arroyo Grande Creek watersheds This site would also control the greatest amount of runoff of all sites considered on this stream system. Two capacities were studied at the Lopez site, including one of £0 5 000 acre-feet The unit cost per acre-foot of yield for this capacity would be about $32 „ The practicability of constructing a dam with such a relatively high unit cost of water would depend to a large degree on the timing of availability of imported water and the unit cost thereof * As stated previously, future increased urbanization of lower Arroyo Grande Valley may dictate the need for flood control storage at the Lopez site as well as downstream channel improvements <, A 50*000 acre-foot reservoir at the Lopez site, operated entirely for water conservation purposes, would still provide appreciable downstream flood control* It can be seen on Plates 11B and Ik that most of the feasible water supply developments in the Coastal Unit are located in the Cambria Subunit while the major portion of present and potential water service areas are in the San Luis Obispo and Arroyo Grande Subunits to the south* Plans for the satisfaction of future supplemental water requirements in the Coastal Unit included conveyance of water through a coastal pipe line, designated the Cambria Conduit, which would be constructed from Upper Ragged Point Reservoir on the north to Indian Knob Terminal Reservoir in the vicinity of San Luis Obispo o The approximate alignment of the Cambria Conduit is shown on Plate lli» At the present time it appears that the proposed Cambria Conduit would lend itself ideally to multibarrel pipe line construction* It is recognized, however, that major modifications in design may be necessary before such a conduit would be built* Certain design factors, such as the conduit location, type of construction, and location of areas to be served, depend upon many physical and economic factors extant in the future which are not susceptible of evaluation at the present time. As in the case of the Nacimiento-Shandon Conduit and Creston Lateral, the timing of need for « supplemental water and the availability of an imported supply and the unit cost thereof, together with the financial capability of the area to be served* will determine which units of the Cambria Conduit, if any, will eventually be constructed, and the order of that construction The proposed Cambria Conduit would begin at the outlet works of Upper Ragged Point Dam at an elevation of about 110 feet. The conduit would then extend southerly along the coast on an alignment roughly paralleling State Highway 1, collecting waters from Yellow Hill, San Simeon, Santa Rosa, and Whale Rock Reservoirso At a point near the town of Morro Bay, the conduit would leave the coast and proceed inland through Los Osos Valley over a low divide into San Luis Valley, and finally terminate at Indian Knob Terminal Reservoir located about five miles south of the City of San Luis Obispo at an elevation of 320 feet° The total length of conduit would be about 5° miles <, Booster pumping plants would be required at Arroyo de la Cruz, San Simeon Creek, Old Creek, and at the low divide between Los Osos and San Luis Obispo Valleys Although detailed estimates of cost of the Cambria Conduit were not prepared, reconnaissance estimates of the cost thereof indicate that the unit cost of water delivered to service areas in the Cambria and San Luis Obispo Subunits would be competitive with the cost of imported water Whale Rock Project It is believed that the solution to the immediate water supply problem facing the City of San Luis Obispo lies in the construction of Whale Rock Dam and Reservoir on Old Creek together with suitable conveyance facilities from the dam to a connection with the City's existing distribution system. The Whale Rock Project and the other developments herein presented for the coastal streams north of Old Creek have the important advantage that they are located in an area of potential water surplus,, Therefore, these developments can be constructed and water exported therefrom to the San Luis Obispo and Arroyo Grande Subunits with adequate allowance for the water needs of the local areas adjacent to these streams « It was found that the Whale Rock Project would have a lower cost for new water yield delivered near the City of San Luis Obispo than would projects on Arroyo Grande Creek, the coastal streams north of Old Creek, or Jack Creek in the Upper Salinas Unit* It should be noted that projects on Arroyo Grande Creek or Jack Creek would be located in local areas of potential water deficiency. It should be further pointed out that, although it appears that the cost of the Whale Rock Project will be higher than that shown herein, this project would provide the best solution to the immediate water supply problem for the City of San Luis 0bispo o Conveyance of water from Whale Rock Reservoir to the City's distri- bution system could best be accomplished by construction of a conduit leading from the dam to the City's filtration plant located in Stenner Canyon at an elevation of 5?6 feet, The proposed conduit is designated herein and is shown on Plate lii as the "Whale Rock Conduit "» For study purposes, a branch lateral, designated the Los Osos Lateral, was also considered which could facilitate the eventual provision of water service to possible future urban areas associated with expansion of the City to the west and south*. The Los Osos Lateral would extend from a proposed bifurcation structure located at the town of Morro Bay to a small terminal regulating reservoir in Los Osos Valley., A small filtra- tion plant would be required to treat water conveyed through the Los Osos Lateral. All units of the Whale Rock Conduit could be incorporated into the Cambria Conduit and would constitute portions of the first barrel of that system? The cost of the Whale Rock Conduit as proposed herein, is estimated to be about $2,,031,OOOc The average annual cost per acre-foot of water delivered to San Luis Obispo would be about $33* of which $1? would represent the cost of conveyance , Detailed cost estimates of the Whale Rock Dam, Reservoir, and Conduit are presented in Appendix Go It might be desirable to effect construction of the Whale Rock Project in staged development • As an initial project to provide assurance of additional water for San Luis Obispo in the immediate future, a small diversion dam with a reservoir storage capacity of 2,000 acre-feet could be constructed at the Whale Rock site, together with a conveyance conduit to the City with a capacity of about 11<>5 second-feet <. This initial dam would also be a zoned earthfill structure, and would be so constructed that it could be later incorporated into the larger dam at the same site* It is estimated that this initial project would provide a firm supply of water to the City of about 2,200 acre-feet per season,, The capital cost of the works would be about $2,150,000, with an average annual cost of the developed water supply delivered to the filtration plant of the City of San Luis Obispo of about $60 per ac re- foot e It should be recognized that with subsequent full development of Whale Rock Reservoir, the unit cost of the water delivered to San Luis Obispo would be reduced to the afore-mentioned value of about $33 per acre-foote Organizational and Financial Aspects of Water Resources Development It is believed that proper implementation of the several water development plans for future construction in San Luis Obispo County, as set forth in this bulletin, will eventually require the formation of a county-wide water agency whose principal functions would be to finance, construct, and operate major water development projects, and to execute water service contracts with subordinate districts „ It is further considered that such an agency is necessary not only to undertake the development of local water resources j but also to obtain imported water from the Feather River Project or some other unit of The California Hater Piano In order to carry out the foregoing objectives, it is believed that either a new agency would have to be created or else additional powers would have to be granted the present San Luis Obispo County Flood Control and Water Conservation District, authorized by Act of the State Legislature in 19k5* These additional powers would include permission for the county-wide agency to sell water and to issue bonds, proceeds from the sale of which could be used for construction of water development projects » In some instances, it would be desirable that these bonds would constitute a lien upon all of the taxable property in the entire County, even though the proceeds thereof might be used to directly benefit a smaller area<> However, concurrently with such financing and construction, the county-wide agency would execute contracts with member units who would be benefited by the project in which the member units would provide sufficient sums to pay off debt service charges on the bonds issued by the county-wide agency, together with operation, maintenance, and replacement costs incurred by the project* With an agency such as San Luis Obispo County Flood Control and Water Conservation District, as modified, in charge of master county water resources development planning and implementation, including financing and construction, the particular local area of a member unit using project water would not be required to raise large funds in advance and would not necessarily require a large staff of qualified personnel to operate and maintain the project or projects o The county-wide agency would also probably have less difficulty in o marketing bonds because of the broadened tax base and resulting increased financial capacity. Thus, the county~wide district might be able to obtain more favorable interest rates and other more favorable bond issuance features than could any of the member units A county-wide water agency would be logically charged with the continuation and expansion of the basic data collection program initiated as part of this investigation* The collection, compilation and -evaluation of basic hydrologic data is absolutely necessary to plan future developments required to maintain adequate water supplies© Plans for Importation of Water It has been shown earlier in this bulletin that the water requirements of potential agricultural lands and urban areas in .San Luis Obispo County exceed the presently developed yields of local sources of water supply o It has been further shown that the yields of all possible local developments considered hereinbefore would fail to meet the estimated ultimate supplemental water requirement of the County by a substantial amount <> As discussed in the introductory chapter of this bulletin, work has been completed on state-wide studies leading to the development of The (California Water Plan, which is a comprehensive plan for the provision of supplemental water supplies to all of the irrigable and habitable areas of the State of California* The initial unit of The California Water Plan, the authorized Feather River Project, and other features of that plan are described in the ensuing sections e Feather River Project The purposes of the Feather River Project are (l) flood control and irrigation in the Sacramento Valley, (2) electric power generation, and (3) to furnish Feather River water for firming surplus waters existing, in most » years, in the Sacramento-San Joaquin Delta. This surplus could be used to provide a supplemental water supply to areas of water deficiency on the west side of the San Joaquin Valley in Fresno, Kings, aid Kern Counties j the south San Francisco Bay areas in Alameda 5 Santa Clara, and San Benito Counties, and the South Coastal Area of Californiac Major units of the Feather River Project, as authorized by the State Legislature in 1951* by Chapter lkkl> Statutes of 1951* included a multipurpose dam and reservoir on the Feather River near Oroville, a power plant at the dam, an afterbay dam and power plant, a Delta Cross Channel, an electric power trans- mission system, a conduit to transport water from the Sacramento -San Joaquin Delta to Santa Clara and iftlameda Counties, and a conduit to transport water from the Sacramento-San Joaquin Delta to the San Joaquin Valley and to southern Californiao It was estimated that about ij, 000, 000 acre-feet of water per season would be provided to areas served by the Feather River Project Aqueduct c Further studies, culminating in the previously described report of the Division of Water Resources entitled "Program for Financing and Construct- ing the Feather River Project as the Initial Unit of The California Water Plan", dated February, 1955* indicated the desirability of certain modifica- tions in the original plan» Among these modifications was the addition of San Luis Reservoir as a major feature of the Feather River Project Aqueduct Several possible routes for the conveyance of water to southern California were discussed in the February, 1955* reporto It was concluded that so-called "High Line Route" would provide the greatest flexibility of all routes studied, as it would serve the greatest water deficient area.. As stated in the introduction of this bulletin, the Legislatures of 1956 and 1957 appropriated funds in the amount of $1,777^000 for studies of alternative routes for the Feather River Project Aqueduct leading from the San Joaquin Valley to southern California, of which $500,000 were designated for studies of a coastal route, -26 Feather River Project water could be delivered to San Luis Obispo County by at least two possible methods , depending upon the alignment finally adopted for the main conduit serving southern California In the event of adoption of the Coastal Line, San Luis Obispo County could be served by direct diversion from various points along the aqueduct as it would traverse the County Although a possible alignment for the Coastal Line was presented in the February , 1955 $ report , final decision as to the most feasible route must necessarily be deferred pending completion of studies currently under way by the Department., In the event of adoption of the High Line Route, San Luis Obispo County could be served by a pumped diversion from that route at a point near Avenal Gap s Since such a diversion was not incorporated in the authorized features of the project, and since firm costs of delivery of water from the project have not yet been determined^ the scheme must be considered only as preliminary in nature <, However, for the purpose of evaluating the economic feasibility of local water supply developments as previously discus sedj, a preliminary cost estimate of such a diversion was prepared in connection with the current investigation,, Under this proposed plan, water would be diverted by a canal side pumping plant located about 10 miles south of Kettleman City The water would be lifted from elevation 370 feet, through five pumping plants and connecting canals, to an elevation of 1,200 feet at the portal of a tunnel through the Diablo Range,, This tunnel would be 5°U miles in length and would discharge into a tributary of Cholame Creek a few miles east of Cholame a Estimates of cost of the foregoing conduit were prepared for con- tinuous diversions of 50, 100, and 200 second-feet into San Luis Obispo County,, A summary of these estimated capital and annual costs is presented in Table 55 o The annual costs were based on an interest rate of three per cent, with a repayment period of 50 years „ Estimates presented in Table 55 refer to costs of the water delivered to the Cholame area and do not include costs of terminal reservoir storage or distribution works within the County*, TABLE 55 ESTIMATED CAPITAL AND ANNUAL COSTS OF FEATHER RIVER PROJECT WATER DELIVERED IN CHOLAME CREEK IN SAN LUIS OBISPO COUNTY Capacity of diversion conduit, in second-feet, and delivered water Item supply, in acre-feet per season —y^ j 100 i 200 3q"75oo~ _73£000 THoTooo" CAPITAL COSTS $8,685,000 $9,5U5 .,000 $11,180,000 ANNUAL COSTS Debt service (50 years at 3 per cent) $ 337,600 $ 371,000 U3U,600 Replacements 8 5 000 11,200 18,U00 Operation and maintenance 173,700 190,900 223,600 Electrical energy 292,000 58MOO 1,168,000 TOTALS $ 811,300 $1,157,100 $ 1,8UU S 600 Annual costs, per acre~foot $ 22 o 20 $ I5o80 $ 12o60 Annual costs, per acre=foot in Feather River Project Aqueduct at point of diversion 8 o 00 8 o 00 TOTALS $ $ 23o80 20,60 Other Units of the California Aqueduct System The authorized Feather River Project is proposed as the initial unit of The California Water Plan and would eventually become the key feature of the California Aqueduct System, a complex combination of works extending from the Oregon line to the Mexican Border It is proposed that more than : . 21,000,000 acre-feet of regulated water would be transported each season through the California Aqueduct System*. The California Water Plan, including features of the California Aqueduct System, are reported on in detail in previously described State Water Resourced Board Bulletin No» 3,. entitled "The California Water Plan" dated May? 1957 Of particular interest to San Luis Obispo County are two features of the California Aqueduct System, namely, the Central Coastal and Carrizo-Cuyama Aqueducts o These two aqueducts would consist of facilities necessary to supply the probable ultimate water requirements of Monterey, San Luis Obispo, and Santa Barbara Counties The Central Coastal Aqueduct would deliver a seasonal amount of 760,000 acre-feet to the foregoing counties c The Carrizo-Cuyama Aqueduct was designed to serve only the C'arrizo Plain and Cuyama Valley areas and would be capable of delivering a seasonal amount of 330,000 acre-feet of water* The Central Coastal Aqueduct would begin at a diversion from the San Joaquin West Side conduit near Avenal Gap e Water would be pumped from the conduit and conveyed westerly to Avenal Gap Forebay, from which it would be lifted through a series of pumping plants and short canals up the easterly slope of the Cholame Hills to a 5 »5-mile tunnel passing westerly through the hills into the Upper Salinas Unit at an elevation of about 1,180 feetc From the westerly portal of the tunnel the aqueduct, in canal, would pass south of the communities of Shandon and Cholame and would discharge into Shedd Canyon Reservoir on Indian Creek. An irrigation supply of 60,000 acre-feet per season would be released for use on lands near the community of Cholame The capacity of this initial reach of the aqueduct would be 2,200 second-feet, or twice the average flow rate, in order to utilize off-peak power, with resultant reduction in costs of electric energy c Shedd Canyon Reservoir would provide regulation for delivery of 160,000 acre-feet per season for irrigation of lands along the easterly slope of upper „ Salinas Valley <> The aqueduct would continue westerly from Shedd Canyon Reservoir to a crossing of Huerhuero Creek where a release of 115,000 acre-feet would be made to Huerhuero Reservoir, which would regulate the supply to a suitable demand schedule for delivery to lands along the upper Salinas River The Central Coastal Aqueduct would then continue from Huerhuero Creek westerly and southerly, passing east of Templeton, Atascadero, and Santa Margarita. An extended series of tunnels , totaling about 16 miles in length, would convey the water from the vicinity of Santa Margarita through the Santa Lucia. Range to Tar Springs Reservoir, located on a tributary to Arroyo Grande Creek, about 8 miles east of Arroyo Grande <, Tar Springs Reservoir would provide regulation for delivery of 30,000 acre -feet per season to the Arroyo Grande Valley and Nipomo Mesa on a monthly demand schedule <= The aqueduct would then continue southerly, releasing 35*000 acre -feet per season for delivery to lands in the Nipomo Valley . After crossing the Cuyama River about 8 miles southeast of Nipomo c, the aqueduct would convey water southeasterly along the edge of Sisquoc Valley to the Sisquoc River* Here 105,000 acre-feet per season would be released into Round Corral Reservoir for regulation and delivery to the Santa Maria Valley . As distinguished from the afore- mentioned Coastal Line of the Feather River Project Aqueduct, however, the Central Coastal Aqueduct would terminate at existing Cachuma Reservoir in Santa Barbara County, and would not be designed to serve areas south of Santa Barbara County <> The locations of features of the Carrizo-Cuyama Aqueduct within San Luis Obispo County are shown on Plate lU» The aqueduct would originate at a canal-side pumping plant on the California Aqueduct in the southwestern corner of the San Joaquin Valley . Water would be lifted up the easterly slope of the Temblor Range to an elevation of 2,500 feet by a series of four pumping plants « The final pump- ing plant would discharge water into two separate pipe lines = One line, the Carrizo Lateral, would continue westward and would discharge into a channel lead- ing through the Elkhorn Plain to Elkhorn Reservoir . The other line, the Cuyama . » teral, would turn southward to Bitterwater Afterbay on Bitterwater Creek, From is afterbay a 4-mile tunnel would pass southwesterly through the ridge to the yama Valley » The pumping plants and aqueduct would be designed so that they old convey the required amounts of water with operation only during periods of f-peak power demand, and would have a capacity of 910 second-feet or twice the srage diversion rate of ^55 second-feet Water supplies in the amount of 76,000 acre -feet per season for Cuyama LLey would be discharged on an off-peak basis from the last pumping plant to tterwater Afterbay which would reregulate them to a continuous flowo All of the nainder of the discharge from the last pumping plant would be discharged into 5 line leading to Elkhorn Reservoir which would provide daily and monthly reregu- bion to make the delivered water supplies conform to the irrigation demand schedule r the Carrizo Plain.. The amount so delivered would be 25^,000 acre-feet per season Implementation of plans for water development described in this and pre- iing sections would provide sufficient water supplies to meet all of the present i probable ultimate water requirements of San Luis Obispo County insofar as can determined at this time<> It has been pointed out that it is probably not practicable to serve water certain irrigable lands in San Luis Obispo County under present economic condi- 3ns because of their elevation or geographic location. The lands in this category ild probably not require water for a considerable period of time in the future is assumed, however, that all of these lands which cannot be feasibly served am local water development works, would eventually be served from an imported ppiy° For summary purposes, there is presented in Table 56 a derivation of the bimated requirements for imported water supplies in Upper Salinas, Coastal, rrizo Plain, and San Joaquin Hydrologic Units under ultimate conditions of devel- nente It will be noted in the table that in excess of 400,000 acre-feet of water old eventually have to be imported to satisfy the ultimate water requirements of e four hydrologic units, e • TABLE 56 ESTIMATED REQUIREMENTS FOR IMPORTED WATER SUPPLIES IN UPPER SALINAS, COASTAL, CARRIZQ PLAIN, AND SAN JOAQUIN HYDROLOGIC UNITS UNDER ULTIMATE CONDITIONS OF DEVELOPMENT In Acre-Feet s Maximum practio able Hydrologic s net safe seasonal yield ; Water s Requirement • a unit s Ground t require- t for imported s water s Surface i Total ? ment i water Upper Salinas l*5,ooa* 31,900 76,900 221,000 iUU,ioo Coastal 21^800 100,100 12^,900 156,200 31,300 Carrizo Plain 600 600 21^6,000 2li5,i400 San Joaquin 7,200 7,200 TOTALS 70,iiOo 132,000 202, LOO 630,^00 1*28,000 * Includes estimated yield of portion of Paso Robles Basin within Monterey County. Flood Control Objectives of the current investigation included a study of flood control problems in San Luis Obispo County,, Although the scope of the current investigation did not permit a comprehensive study of the problem, sufficient data were available to ascertain that flood control is not presently a major problem in the County, except in the Arroyo Grande and Santa Maria Valleys c Throughout the rest of the County, flood hazards consist of minor flooding and drainage problems „ During periods of heavy runoff, damage in the latter areas is generally limited to erosion of highway fills and bridge abutments State funds were provided by the Legislature in 1936 and again in 1952 to a number of counties, including San Luis Obispo County, for the emergency repair of various highway fills, bridges, and culverts damaged or washed out by floods occurring in those years -272- . , - Historical flood damage of major proportions in -San Laiis Obispo County was sneral ly confined to lands comprising flood plains of the upper Salinas River rroyo Grande Creek, and the Santa Maria River, and consisted of channel bank ero- ton and extensive damage to agricultural property, railroads, highways, residences, isinesses, industries, public property, and utilities. Because of relatively short records of stream flow in San Luis Obispo Dunty, peak discharges resulting from most floods can only be estimated from high- iter marks , newspaper accounts , and other available sources » Available data indi ate that at least eight floods of major proportions occurred in San Luis Obispo Dunty since the flood of 1861-62, the earliest known major flood of recent history. t least 12 other floods of lesser magnitude than the foregoing caused considerable mage to both public and private property . It is anticipated that the extent of image resulting from a repetition of floods of magnitudes comparable with the *regoing, will increase as more intensive urban ^ industrial , and agricultural de= jlopment occurs on flood plains adjacent to stream channels. Presented in the following paragraphs, under their respective section ladings, are discussions of flood control problems and existing improvements in le three major flood hazard areas of San Luis Obispo County pper Salinas River Valley In terms of peak discharge, the flood of 1938 was the largest of record 1 the upper Salinas River* A peak flow of 11,000 second-feet was recorded at the . So Geological Survey gaging station near Santa Margarita in February of that sar Although the flood of 1862 may have been one of greater magnitude, suffi- Lent data are not available to evaluate its peak discharge « Other floods, includ- ag those of l88l, 1889, 1890, 1911, and 1937, are reported to have been especially irge« A peak flow of 7^260 second-feet was recorded at the Salinas River gaging tation near Santa Margarita in February, 1937° The major portion of damage from the foregoing floods in the Upper Salinas River Valley was generally limited to bank erosion and consequent loss of agricul- tural lands o The Salinas River channel near Paso Rohles was eroded and considerably widened in places as a result of the 1862 flood* Damage to public property occurred during the 1913-1*4- flood when the highway bridge at Paso Robles and a railroad bridge near the Monterey County line were washed outo There are no flood control works at the present time in the Upper SalinasJ River Valley. Some degree of protection for downstream lands and property is afforded by Salinas Reservoir which provides incidental regulation of peak dis- charges of the upper Salinas River Since construction of the dam and reservoir in 1S&1> damage to lands adjacent to the river has been negligible and limited gener- ally to minor bank erosion. Based on the foregoing data, it is not believed that construction of flood control works would be justified at this timeo The presence of brush and trees in the channel which, it is reported, have increased in areal extent since the construc- tion of Salinas Dam, may pose a minor flood hazard The feasibility of clearing the channel is questionable^ since the cost of clearing could be considerably greater thai the flood control benefits which would be derived therefrdm* Such a project would result in a saving in water, however, through reduction of nonbeneficial consumptive use of water by phreatophytes <> Arroyo Grande Valley The floods of 1909 and 1911 are reported to be the largest known to have occurred on Arroyo Grande Creek*. These floods produced estimated peak discharges of 28,000 and 30,000 second-feet, respectively, at the town of Arroyo Grande, based on high-water marks » These floods caused substantial damage to public and private property and resulted in the loss of three lives. Other floods, including those of 1862, 1884, I89O, 1914, 1937, and 19^3, though of lesser magnitude than the 1911 -. , » - - lood, caused extensive damage to both public and private property o It is inter sting to note that the storm of February and March., 1938j> which caused sraeh exp- ensive damage throughout the rest ©f central and southern Californiag ©eased only =gligible damage in Arroyo Grande Valley* The most recent flood of consequence on Arroyo Grande Creek was that tiich occurred during the 1951-52 season . This flood produced a peak flow of 5>3?0 econd-feet at the U» So Geological Survey gaging station at Arroyo Grande, and aused minor damage to the channel banks 6 Approximately 300 acres of agricultural ands were inundated and one bridge was damaged The greatest potential flood hazard in Arroyo Grande Valley appears to 3 to those lands comprising the rich flood plain of the lower valley below the ity of Arroyo Grande o Lands above Arroyo ' Grande are also subject to flooding, Lthough to a lesser degree than the lower valley lands. Efforts have been made to ontrol flood flows in lower Arroyo Grande Creek by the construction of levees along oth sides of the channel These levees extend from a point a few hundred feet bove State Highway 1 to the mouth of the creek channel, just west of the town of ceanoo Certain critical sections of the levees have been reinforced with post and Ire revetment , Unfortunately , these levees were constructed of highly erodable, ow~density, sand and gravel,, and are frequently breached during flood flows. The extent of flood hazard in lower Arroyo Grande Valley is difficult to valuate because of limited available data and changing channel conditions . For he two foregoing reasons and because of the lack of good correlation between peak ischarge estimates and resulting flood damage, the evaluation of potential flood amage is subject to considerable error. The problem can best be illustrated by a omparison of flooded areas resulting from two recent floods . The 1952 flood, with peak flow of 5? 370 second-feet, as stated previously, flooded approximately 330 cres of land. By contrast, the 19*+3 flood, with a peak flow of only 2,800 second eet, flooded nearly 400 acres in the same area . * Maximum nondamaging discharges of Arroyo Grande Creek have "been estimated by both the U. S. Corps of Engineers and the Arroyo Grande Soil Conservation Dis- trict in connection with the preparation of previously discussed reports <> In their 19^1 report, the Corps of Engineers estimated that the maximum nondamaging flows in Arroyo Grande Creek for the upper and lower valley reaches were 9,000 and 3,000 second-feet, respectively,, Based on data contained in the 1955 report of the Arroyo Grande Soil Conservation District, it was estimated that the maximum nondamaging flood flow in lower Arroyo Grande Creek would be only slightly greater than 1,300 second-feet Possible plans for the control of floods in Arroyo Grande Valley invest! gated by the U» S. Corps of Engineers included; (l) a dam for flood control only at the Lopez site, and levees in the lower valley along lower Arroyo Grande Creek and its principal lower tributary, Los Berros Creek, (2) a dam for flood control and water conservation at the same site, and levees in the lower valley identical with those in the first plan, and (3) levees in the lower valley * The first of the' three foregoing plans was considered by the Corps of Engineers to be the most ad- vantageous and was estimated to have a total capital cost of $U, 3^5*000 and an annual cost of $189, 000, At the time of completion of their report, the Corps of Engineers found that there was not presently economic justification for any of the three plans studied since the estimated annual cost of each of the plans would have been approximately four times the average annual tangible benefits, and because in- tangible benefits would not have been sufficient to outweigh the lack of economic justification.. Because of continued local concern over the existing threat of damage from floods, Zone 1 of the San Luis Obispo County Flood Control and Water Conserva- tion District was formed in lower Arroyo Grande Valley in 19^5 • In 1951* residents of Zone 1 successfully voted a bond issue in the amount of $^0,000o It was intended that the $^0,000 would be used for the construction of flood control works in lower Arroyo Grande Valley, although no construction work has been started An investigation of a plan for works of improvement in the Arroyo Grande watershed was completed in 1955 by the U« S. Soil Conservation Service, under the direction of and in cooperation with the Arroyo Grande Soil Conservation District and the San Luis Obispo County Flood Control and Water Conservation District;, as authorized by the Watershed Protection and Flood Prevention Act (Public Law 566, 83rd Congress, 68 State, 666 )<, Results of the investigation were reported on in the previously cited report of October, 1955 i of the two afore-mentioned districts The report proposed a plan for a combination of land treatment and structural measures at an estimated total cost of $k75,31$> of which it was proposed that $3ll9*895 would be borne by the Federal Government, and $125^20 would be borne by local interests. Structural measures, designed to prevent overflow of Arroyo Grande Creek and its principal lower valley tributary, Los Berros Creek, included channel realignment and enlargement, in addition to embankment stabilization Based on the engineering and economic analyses presented in the report, it was concluded that the project as proposed, would have an over-all favorable benefit-cost ratio of 1 2U to 1<> Construction of a portion of this project was completed in 1957© -277* Although it was not possible to make an independent analysis of all flood control aspects in Arroyo Grande Valley in connection with the San Luis Obispo County Investigation* certain flood control aspects of a dam and reservoir located at the Lopez site were studiedo Results of these studies indicate that a flood peak regulated by the surcharge storage in a 50,000 acre-foot capacity reservoir, assuming the reservoir full at the beginning of the flood flow, would reach the lower valley considerably later than the peak flow from the tributary area below the dam It was further found that the resulting peak outflow from Lopez Reservoir would be essentially equivalent to the peak discharge from the lower tributary area and that the two peak flows entering the lower valley would be from two to four and one-half times the carrying capacity of the channel . It will be noted that even with greater control of the peak flows at Lopez dam site, which a flood control reservation would provide, the peak flow from the tributary area downstream from the reservoir, if no regulatory storage were constructed on the streams draining therefrom, would exceed the downstream channel capacity,, Therefore, it appears that consideration of a flood control reservation in the reservoir would not be justified*. It further appears that the most effective means of providing flood control on Arroyo Grande Creek would be by channel improvements at such time as they would be economically justifiedo Santa Maria River Valley The largest peak discharge of record on the Santa Maria River and its tributaries occurred as a result of the March, 1938, floods A peak flow of 17,300 second-feet was recorded at the U.S. Geological Survey gaging station on the Santa Maria River near Santa Maria during that flood. Although exact comparisons cannot be made, it is believed that the flood of 1862 was probably of the greatest magnitude in recent history. Other floods causing extensive o amage in Santa Maria Valley included those of 1878, 1881*, 1890, 1909, 1910, 1931, ?ll*, 1921*, and 1937° All of the foregoing floods caused extensive damage to or 3ss of agricultural lands and would cause even greater damage if they were speated under present conditions of development. The City of Santa Maria was ictensively flooded during several of the foregoing peak flows. The most critical flood hazard in San Luis Obispo County, as well as Ijacent Santa Barbara County, is believed to be that which presently exists in le Santa Maria Valleyo A repetition of any of the previously cited floods would amage or destroy lands and property throughout the valley „ Flood control works Long the Santa Maria River consist primarily of low training dikes constructed at irategic points o A rail and wire revetment was constructed along the north bank I the river by the County of San Luis Obispo in 1953 at a total cost of $7,000 o lese measures offer a moderate degree of protection from small floods, but, at sst5 can offer only temporary protection from most of the damaging floods which ive caused such havoc in recent years c It is believed that adequate flood control measures for the Santa Maria illey are incorporated in the authorized Santa Maria Project currently under >nstruction c The Santa Maria Project is a water conservation and flood control reject which was jointly developed by the U. S. Bureau of Reclamation and Corps r Engineers, and consists of a dam at the Vaquero site on the Cuyama River about Lx miles upstream from the confluence of the Cuyama and Sisquoc Rivers, together Lth levees along the Santa Maria River and a portion of a tributary stream, *adley Canyon » The location of Vaquero Reservoir is shown on Plate ll* c The Santa Maria Project is presently being constructed jointly by the . So Bureau of Reclamation and Corps of Engineers, and is scheduled for completion i 1959c The proposed dam is designed as a zoned earthfill. It would have a height F 181* feet above stream bed and would have a crest length of 1,775 feet„ The PTC o reservoir would cover an area of 3^00 acres and •would impound 214,000 acre -feet of water to the top of the spillway gates* The Vaquero Dam and Reservoir is a multiple -purpose development having storage allocations as follows: Silt storage ^5,000 acre -feet Flood control reservation 89^000 acre -feet Conservation storage 80,000 acre-feet The Santa Maria Valley Levee and Channel Improvements are described in Appendix 3 to the report of the District Engineer, Corps of Engineers, Los Angeles District, dated June 15^ 1951; as follows: . - "17 « Locat ion and JTuncit ion -The Santa Maria Valley levee and channel improvements consist of the following: (l) Levee and channel improvements along Santa Maria River and (2) levees and an excavated channel extending from the canyon mouth of Bradley Canyon to a point on Santa Maria River about 3»3 miles downstream from Fugler's point "l8o The levee and channel improvements along Santa Maria River would consist of the following: (l) A single levee extending along the left bank of Santa Maria River for about 17 miles from Fugler's Point to a point about 600 feet downstream from the highway bridge at Guadalupe, (2) a single levee extending along the right bank of Santa Maria River for about 5 miles from a point about 1-l/U miles downstream from the Highway US 101 bridge to a point about 1-1/2 miles upstream, from the railroad bridge at Guadalupe, and (3) channel clearing from Fugler's Point to the Pacific Ocean « Upstream from the upper end of the right -bank levee, the channel would be cleared between the levee on the left bank and the edge of the right banko Between the upper end of the right -bank levee and Bonita Road, the channel would be cleared between the levees. Below Bonita Road, clearing would be limited, in general, to a 1,500-foot wide channel., "19 • The Bradley Canyon levee and channel would consist of 2,600 feet of double levees along the lower end of the work and 7.>500 feet of single levee. In addition, a 1,500-foot dike would be constructed along the right bank at the mouth of the canyon to prevent the inunda- tion of high-valued agricultural and residential property ." These levees would have an l8-foot crown and vary in height from 10 to Ik feet above stream bedc A6 described in the Corps of Engineers ' report on the Santa Maria Project the proposed project would control to nondamaging intensity a design flood peak of 230,000 second-feet in the Santa Maria River Operation of Vaquero Reservoir would ^280- . . sduee the design peak to 150,000 second-feet at Fugler's Point » Below Fugler's Dint the proposed channel improvements are designed to safely pass 150,000 second- jet. In the report of the U» S» Bureau of Reclamation entitled, "Santa Maria reject, Southern Pacific Basin, California", dated November 30,, 1951, the total sst of the project was estimated to he $24,575,000, cased on October, 1950, price jvelso A summary of project costs is as follows; Vaquero Dam and Reservoir $1^,300,000 Santa Maria River levees 9,5^0,000 Bradley Canyon levees 735.? 000 TOTAL $2^,575,000 In addition to the cost of the flood control levees, the estimated allo- ition to flood control of the cost of Vaquero Dam is $3,530,000, making a total Lood control allocation for the project of $13,805, 000c Of this amount, the fed- :al agencies recommended that local interests contribute $990,000 toward the cost I levees and channel improvements in the Santa Maria Valley, which cost represents jquisition of lands, easements, rights of way, and relocation of utilities neces- ary for construction of channel improvements o The remainder, or $12,815,000, was ^commended to be nonreimbursable » An amount of $10,770,000 was allocated to water snservation and would be repaid to the Federal Government by local water users Pursuant to Chapter 13, Statutes of 1957, approved by the Governor on ebruary 1, 1957, the Santa Maria Project, as recommended by the Chief of ngineers in House Document Numbered ^00, Eighty-Third Congress, Second Session, as adopted by the State Legislature as an approved water development project, his approval by the State Legislature authorizes appropriations to be made by he State to pay for that portion of the cost of local cooperation which includes urchase of lands, easements, and rights of way, and replacement of existing ridges and utilities . CHAPTER V. SUMMARY OF CONCLUSIONS AND RECOMMENDATIONS As a result of field investigation and analyses of available data on the water resources and water problems of San Luis Obispo County, the following conclusions and recommendations are made. Summary of Conclusions 1. Recent growth of population and irrigated agriculture within San Luis Obispo County has resulted in increased demands on both surface and underground water resources. 2. Anticipated future growth of population and irrigated agriculture will require an extensive program of development of local water resources, and full satisfaction of the ultimate water using potential of the County will require importation of substantial amounts of water from sources outside of the County. 3» The present primary source of water supply of San Luis Obispo County is direct precipitation. The occurrence of precipitation' in the County varies markedly both areally and with time, mean seasonal depth of precipita- tion varies from a maximum of about k2 inches in the Santa Lucia Range to about eight inches on the Carrizo Plain* Approximately 90 per cent of the seasonal precipitation generally occurs during the six -month period from November through April . Precipitation from season to season varies generally from as low as about 25 per cent to as much as about 220 per cent of the mean seasonal amount 4. Surface runoff of streams draining San Luis Obispo County follows closely the pattern of occurrence of precipitation both monthly and seasonally. . 5- With the exception of the regulation of the Salinas River afforded by operation of Salinas Reservoir, regulation of the water supplies of San Luis Obispo County has, to date, been accomplished almost entirely through utilization of storage in underground reservoirs. The recently com- pleted Nacimiento Reservoir will serve to regulate the flow of Nacimiento River and will provide supplemental water for beneficial use in Monterey County. Vaquero Reservoir, presently under construction, will regulate flood flows of the Cuyama River and make possible increased recharge of the Santa Maria ground water basin, thereby reducing the present overdraft in that basin. 6„ Salinas Reservoir, the property of the United States Army, with a gross storage capacity of 26,000 acre-feet and an estimated net safe seasonal yield of 5>600 acre-feet, presently provides seasonal water supplies of up to 3>000 acre-feet to the City of San Luis Obispo. In addition, intermittent releases have been made from the reservoir to the Salinas River at the request of downstream water users. 7° A total of 19 ground water basins varying in economic importance have been identified in San Luis Obispo County, excluding the Santa Maria and Cuyama Basins, and it is estimated that in excess of 200,000 acre-feet of underground storage capacity has been utilized to date in those basins. The safe yield of the presently developed ground water supply, excluding the Santa Maria and Cuyama Basins, is about 41,100 acre-feet per season, distributed by hydrologic units as follows 1 Upper Salinas Unit, 26,900 acre-feet; Coastal Unit, 13,600 acre-feet; Carrizo Plain Unit, 600 acre-feet; and San Joaquin Unit , none 8. Surface and ground water supplies of San Luis Obispo County are generally of fair to good mineral quality and suitable for irrigation and other beneficial uses Surface and ground water supplies from certain localized areas are relatively hard and also exhibit relatively high concen- trations of total dissolved solids, sulphates, and boron* 9o The urban and agricultural areas presently receiving water service in San Luis Obispo County comprise about 3li>000 acres, distributed by hydrologic units as follows; Upper Salinas Unit, 12,000 acres; Coastal Unit, 12,000 acres; Santa Maria Unit, 6,000 acres; Cuyama Unit, 1^,000 acres; Carrizo Plain Unit, 300 acres; and San Joaquin Unit, none 10o It is estimated that, under probable ultimate conditions of development and water use in San Luis Obispo County, there would be about 333,000 acres requiring water service, distributed by hydrologic units approximately as follows: Upper Salinas Unit, 117,000 acres; Coastal Unit, 71,000 acres; Santa Maria Unit, 16,000 acres; Cuyama Unit, 27,000 acres; Carrizo Plain Unit, 100,000 acres; and San Joaquin Unit, 2,000 acres e 11<. The present mean seasonal water requirement of San Luis Obispo County is about 69*000 acre-feet, distributed by hydrologic units as follows: Upper Salinas Unit, 27,000 acre-feet; Coastal Unit, 16,000 acre-feet; Santa Maria Unit, 17,000 acre-feet; Cuyama Unit, 8,000 acre-feet; Carrizo Plain Unit, 600 acre-feet; and San Joaquin Unit, none<> 12e The probable ultimate mean seasonal water requirement of San Luis Obispo County will be about 721,000 acre-feet, distributed by hydrologic units as follows: Upper Salinas Unit, 221,000 acre-feet; Coastal Unit, 156,000 acre-feet; Santa Maria Unit, 28,000 acre-feet; Cuyama Unit, 63,000 acre-feet; Carrizo Plain Unit, 21*6,000 acre*feet; and San Joaquin Unit, 7,000 acre-feet, 13 « There is no present requirement for supplemental water in San Luis Obispo County except in the Santa Maria Unit, wherein an overdraft on the underlying Santa Maria Ground Water Basin exists Present and ultimate -28 U supplemental water requirements were not derived for the Santa Maria and Cuyama Units since the U. S. Geological Survey is presently engaged in detailed hydrologic studies of the Santa Maria and Cuyama Ground Water Basins,, Results of these studies will provide valuable data for the future re-evaluation of the safe yields of the foregoing ground water basins liic It is considered that of the remainder of San Luis Obispo County, excluding the Santa Maria and Cuyama Units, future urban and agri= cultural and development will first result in water deficiencies in the Upper Salinas Unit and the San Luis Obispo and Arroyo Grande Subunits of the Coastal Unite 15 e Under probable ultimate conditions of development and water use in the portion of San Luis Obispo County which excludes the Santa Maria and Cuyama Units the mean seasonal requirement for supplemental water will be about 583*000 acre-feet c 16<> Approximately 155*000 acre-feet of supplemental water can be developed seasonally from local water supply sources in San Luis Obispo County, including about 29*000 acre-feet from ground water sources and 126,000 acre- feet from surface water developments o The portion of the ultimate supplemental water requirements of San Luis Obispo County which cannot be met through further development of local water supply developments could be supplied •through importation facilities of the California Aqueduct System, a major feature of The California Water Piano 17 * In order to accomplish maximum practicable development of local surface water supplies of San Luis Obispo County the undeveloped dam and reservoir sites considered to be most favorable for development, with respect to both cost and yield of water, include the following? Site Stream Lower Jack Jack Creek Santa Rita Santa Rita Creek San Miguelito NacintLento River Jarrett Shut-in Nacimiento River Bald Top San Carpoforo Creek Upper Ragged Point San Carpoforo Creek Yellow Hill Arroyo de la Cruz San Simeon San Simeon Creek Santa Rosa Santa Rosa Creek Whale Rock Old Creek Lopez Arroyo Grande Creek 18 e The Lower Jack, Santa Rita, San Miguelito and Jarrett Shut-In Dams and Reservoirs could provide supplemental water supplies to lands in the Upper Salinas Unit, It is feasible from an engineering standpoint to convey water conserved by the San Miguelito and Jarrett Shut-In Reservoirs by means of a pressure conduit to potential water service areas in the Upper Salinas Unit. 19. The Bald Top, Upper Ragged Point, Yellow Hill, San Simeon, Santa Rosa, Whale Rock, and Lopez Dams and Reservoirs could provide supplemental water supplies to lands in the Coastal Unit* It is feasible from an engineering standpoint to convey water conserved by Bald Top, Upper Ragged Point, Yellow Hill, San Simeon, Santa Rosa, and Whale flock Reservoirs by means of a pressure conduit to potential water service areas in the Cambria and San Luis Obispo Subunits* 20* The most pressing water resource problem facing San Luis Obispo County is considered to be the development of an additional water supply for the City of San Luis Obispo Existing sources of supply will be inadequate to meet the City's increasing demands for water by about 1960 o 21* The Whale Rock Project on Old Creek, including a conveyance conduit leading to the City of San Luis Obispo's existing filtration plant could be constructed as the initial feature of the plan presented in this S&6* bulletin for conservation of local surface water supplies of San Luis Obispo County c 22 „ If constructed, the Whale Rock Project would provide sufficient water for the City of San Luis Obispo until 1990, and in addition could serve water to intermediate areas between the reservoir and the City, provided the City maintains its present supply in Salinas Reservoir This project would have a capital cost of about $h 9 91S$000 } including the dam and reservoir and conveyance conduit to the City of San Luis Obispo, and would deliver water to the City at a cost of about $33 per acre=footo 23 o A staged construction of the Whale Rock Project may be desirable., whereby a diversion dam and conduit would be constructed initially, at a capital cost of about $2 5 l50^000o This initial project would provide a firm water supply of about 2,200 acre-feet per season at a unit cost of about $60 per acre=footo 2ljo Water required to meet anticipated future water needs of San Luis Obispo County, in excess of that which can be conserved by full practicable development of local waters, can be made available through facilities of The California Water Plan The authorized Feather River Project is the initial unit of that plan n 25° Flood hazards presently exist in the Santa Maria and Arroyo Grande Valleys, but flood control is not a major problem in the remainder of San Luis Obispo County,, The Santa Maria Project, presently being constructed by the U. S. Bureau of Reclamation and the Corps of Engineers, U.S. Army, will provide flood control in the Santa Maria Valley as well as alleviate ground water overdraft in the Santa Maria Ground Water Basin. Studies of flood control works for protection of Arroyo Grande Valley have been conducted by the Corps of Engineers and the U. S. Soil Conservation Service. . s 26<> The prosecution of a sound, comprehensive program of water resources development in San Luis Obispo County will require formation of a single county-wide water agency^ organized with appropriate powers. Such an agency will be necessary to properly undertake the development of both local and imported water supplies. Recommendations It is recommended lo That the existing San Luis Obispo County Flood Control and Water Conservation District be granted additional authority or that a new county~wide agency endowed with appropriate powers^ as set forth hereinbefore, be created for the purposes of planning, coordinating, financing, constructing, and operating feasible water supply developments <. 2c That plans for the development of the local water resources of San Luis Obispo County be executed in conformity with the conclusions set forth herein* 3° That a program be initiated for the acquisition of lands, easements, and rights of way necessary for construction of feasible water supply developments in San Luis Obispo County described hereinbefore ii. That a program involving the collection, compilation, and evaluation of basic hydrologic data throughout San Luis Obispo County be continued and expanded for the purpose of more adequately evaluating the water problems and solutions thereto under continuing growth and development of the County. 5° That continuing support be given to the study of major multi- purpose water resources developments under The California Water Plan, including those relating to importation of supplemental water to central and southern California '?- • 2 PLATE I STATE OF CALIFORNIA DEPARTMENT OF WATER RESOURCES DIVISION OF RESOURCES PLANNING SAN LUIS OBISPO COUNTY INVESTIGATION LOCATION OF SAN LUIS OBISPO COUNTY SCALE OF MIlES A50NAL PHECIF 21 6B INCHES PASO ROBLES SAN LUIS OBISPO RECORDED SEASONAL P R E C I P ITATION PASO ROBLES SAN LUIS OBISPO ACCUMULATED DEPARTURE FROM MEAN SEASONAL PRECIPITATION REPRESENTATIVE PRECIPITATION CHARACTERISTICS IN SAN LUIS OBISPO COUNTY DEPARTMENT OF WATER RESOURCES 7" A > o r~ V STREAM GAGING AND WATER SAMPLING STATIONS 1954 2 g MEAN SEASONAL NATURAL RUNOFF, 224,600 ACRE-FEET MEAN SEASONAL NATURAL RUNOFF.23,900 ACRE-FEET MEAN SEASONAL NATURAL RUNOFF, 46,300 ACRE-FEET v> DRAINAGE AREA, 354 SOUARE MILES DRAINAGE AREA, 106 SQUARE MILES DRAINAGE AREA, 41 4 SQUARE MILES a UNIT SEASONAL NATURAL RUNOFF, 635 ACRE-FEET PER SQUARE MILE UNIT SEASONAL NATURAL RUNOFF, 225 ACRE-FEET PER SQUARE MILE UNIT SEASONAL NATURAL RUNOFF, 1120 ACRE-FEET PER SQUARE MILE 2 J < ill il 1 1 . l.i . Illl ! " ' joo | 1 ; 1 ll 1 1 1 J 1.. 1 1, 19 1. 1 llliilll 1 .illl i.lllill.ilii.,llJli.,iiili jJ.Jlli.liLi ii... U ..lil ill II J 1 Jill J ARROYO GRANDE AT ARROYO GRANDE NACIMIENTO RIVER NEAR SAN MIGUEL CREEK ARROYO DE LA CRUZ NEAR SAN SIMEON ESTIMATED UNIT SEASON AL NATURAL RUNOFF LLLUJeLIL z /] \/i Z I I W< o K / ' tc l\] Sj ' s !L a/ ^\ u \ J^-P^'S lj /\r* s {'\ , K j *''\ o / \ \ t\[* \ l\rJ^ f'\ N s? ^"' ' IK \ \y J \ \.~r \ 2 S / < -400 | «-- BASE PERIOD —+ * BASE PERIOD BASE PERIOO * -SCO II II II II Illl llliilll II llllll Mill NACIMIENTO RIVER NEAR SAN MIGUEL ARROYO GRANDE CREE < AT ARROYO GRANDE ARROYO DE LA CRUZ NEAR SAN SIMEON ACCUMULATED DEPARTURE FROM ME AN SEASONAL NATURAL RUNOFF REPRESENTATIVE RUNOFF CHARACTERISTICS IN SAN LUIS OBISPO COUNTY A C % DEPARTMENT OF WATER RESOURCES SAN LUIS OBISPO COUNTY INVESTIGATION COASTAL AND SANTA MARIA HYDROLOGIC UNITS AREAL GEOLOGY 1954 PLATE 7-C DEPARTMENT OF WATER RESOURCES SAN LUIS OBISPO COUNTY INVESTIGATION CUYAMA, CARRIZO PLAIN AND SAN JOAQUIN HYDROLOGIC UNITS AREAL GEOLOGY 1954 > 3 S 3* V v C? »™ ° a 5 NORTHEAST SilM X 8 N , K 8 t sS g s £ |s l ||S 1 S I = S 1 j'S s IS "SiS" S s 2 I ° % \ 8 | Ba " S s $ n% § ,» i 1 5 „a„oo„ '"^-V- PASO 1 J " 1 IOO =; SSi / I0p 1 \ Jlfe sw 3 s=3 ~Th *® £ IfT^ TQp ! h B TQp 1 TQp 1 1 ( 1 =8 1 Ik M "x 1 -s _| i-__ i P \i -^ P ' ^^ 1 ^^" DEPARTMENT OF Wi **" M "' SAN LUIS OBISPO COUNTY INVESTIGATION GEOLOGIC CROSS SECTIONS B A-A'. B - '. C-C'AND D-D' I °p^ r? 1955 $ % $ S G' IS 2 m !•> <*s 5 rt 200 200 PACIFIC OCEAN GROVER CM SEA LEVEL II '"" TQp TQp (?) 200 -200 - -200 -200 • Qal i- TQp j£ -400 -400 -400 -400 Qsr Qso TQp Pc Mv \ Tu JK DEPARTMENT OF WATER RESOURCES SAN LUIS OBISPO COUNTY INVESTIGATION GEOLOGIC CROSS SECTIONS E-E', F-F'.G-G'.H-H'AND J-J' 1955 — Z7~ |) ^ ^j -/ /7~^ J s c J^' -^'-L ,'\ / 6 ^rT* ' [CHORRQ BASIN -- SAN LUIS obispo "^V BASIN f -\ an \ P A C I F I C OCEAN DEPARTMENT OF WATER RESOURCES SAN LUIS OBISPO COUNTY INVESTIGATION COASTAL AND SANTA MARIA HYOROLOGIC UNITS LINES OF EQUAL ELEVATION OF GROUND WATER FALL, 1954 PASO ROBLES BASIN MORRO BASIN ALLUVIUM WELL 29 S/ IE 9PI GROUNO URFACE EVAT KELL 28S/I2E IOR2 GROUND SURFACE ELEVATION BOO El 10 i 78.1 /s / s \ ,/\ *->> / / \ ~\ / L, / 1 rv / \ ^ Ir Ir A 1 / A ; /Ajvj V h / N '" \ -* X i\ / i \ / V / N.^' V / / / ~- PERIODS OF FLOW IN SALINAS RIVER AT PASO ROBLES / 1933 34 1935 36 37 38 39 1940 4 1 42 43 44 1945 46 47 48 49 1950 51 52 53 54 1955 1945 46 47 48 49 1950 51 52 53 54 1955 R= RELEASE FROM SALINAS RESERVOIR ARROYO GRANDE BASIN WELL32S/I3E23F Gfi OUND SURFACE ELEVA1 ION 161 z 20 10 "\ \ \aa ' PASO ROBLES FORMATION f\ 1 i - J\ A / L Vft 1 -N WELL 26S/I4E I6LI GROUN D SUfiFA CE ELEVATION 1016-0 \ \ O 4 %V 1950 51 52 53 54 1955 SURFACE i O 1952 53 54 1955 1952 53 54 1955 / O / \ •-/ \ / r^v f ROUND >~S/ 3 1950 51 52 53 54 1955 49 1950 51 52 53 54 1955 1 I I WELL32S/I3E 28AI GROUNO SURFACE ELEVATION 101.9 N — --_ 1953 54 1955 --- - — ---- __ ___. A. aJ — —./ V 1933 34 1935 36 37 38 39 1940 41 42 43 44 1945 46 47 48 49 1950 51 52 53 54 1955 WELL32S/I3E28GI G ROUND SURFACE E LEVATIO N 864 1 NOTE! ELEVATIONS REFERRED TO U.S.G.S. r DATUM INTERPOLATED LEVELS INDICATED BY DASHED LINE. ~-^ 1 ^^^ --.. . ^_ / | f o IVV \S \, P o -J \J — ' p p ) o P "X Ir p o o p p P p 1 o i O Q V % * P o P p p i 1953 54 1955 1952 53 54 1955 1937 38 39 1940 41 42 43 44 1945 46 47 48 49 1950 51 52 53 54 1955 P= WELL MEASURED WHILE PUMPING FLUCTUATION OF WATER LEVELS AT SELECTED WELLS DEPARTMENT OF WATER RESOURCES DEPARTMENT OF WATER RESOURCES SAN LUIS OBISPO COUNTY INVESTIGATION COASTAL AND SANTA MARIA HYDROLOGIC UNITS PRESENT AND PR08ABLE ULTIMATE LAND USE 1954 MEAN SEASONAL PRECIPITATION, II. 26 INCHES FE8 MAR APR MA* JUN JUL AUG SEP OCT NOV DEC JAN FEB MAR APR MAY AUG SEP OCT NOV DEC MONTHLY PRECIPITATION, SHANDON AND VICINITY MEAN SEASONAL CONSUMPTIVE USE OF WATER, 4656 INCHES MEAN ~ SEASONAL CONSUMPTIVE USE OF WATER, 41. 36 INCHES F NORMAL IRRIGATION SEASON U— NORMAL IRRIGATION SEASON -W p™ ! r n 1 | n; j. : i H i rl ] [ | -1 4 ; : iUI in \ AUG SEP OCT NOV DEC JAN FEB MAR APR MAY JUN JUL AUG SEP OCT NOV DEC MONTHLY CONSUMPTIVE USE OF WATER BY ALFALFA, MONTHLY CONSUMPTIVE USE OF WATER BY ALFALFA, SHANDON AND VICINITY SAN LUIS OBISPO AND VICINITY tEAN SEASONAL CONSUMPTIVE USE OF WATER, 29 57 INCHES MEAN SEASONAL CONSUMPTIVE USE OF WATER, 29.73 INCHES h- ORMAL IRRIGATION SEASON H -NORMAL IRRIGATION SEASON | II j „ MAY JUN JUL AUG SEP OCT NOV DEC MONTHLY CONSUMPTIVE USE OF WATER BY TRUCK CROPS, MONTHLY CONSUMPTIVE USE OF WATER BY TRUCK CROPS, SHANDON AND VICINITY SAN LUIS OBISPO AND VICINITY CONSUMPTIVE USE OF APPLIED WATER TOTAL MONTHLY CONSUMPTIVE USE CONSUMPTIVE USE OF PRECIPITATION MONTHLY DISTRIBUTION OF MEAN SEASONAL CONSUMPTIVE USE OF WATER BY REPRESENTATIVE CROPS, SAN LUIS OBISPO COUNTY DEPARTMENT OF WftTER RESOURCES PLATE. 1 3 • • • • • • • • « • • *- W , RIOD OF R ^ F PROJECT ^ • • • * • • • • • • • • • • • 1 • • • • • • X • • • • • • 1 • • X • • X • • X • X • • o • z < 3 X • 1- f Z WA FER REQUIR EMENT • Z • o \ ^h _l • o0. A. i ^POPUL ATION 1880 1890 1900 1910 1920 1930 1940 1950 I960 1970 1980 1990 2000 YEAR PROJECTION OF POPULATION AND WATER REQUIREMENT OF CITY OF SAN LUIS OBISPO DEPARTMENT OF WATER RESOURCES \ S4 KING CITY Rase -: - - -^ Jc^^5s=^x 5 V.,...y...,J c vv p «°^ ^Ix-T^-— . J/ > x \ -«o _|- * UOW6R JACK RgSEKVOIB » ^^ jni'/*"--M"' 3f/>EXISTlNC S«N LUIS 08BP.O /V. „u^ ^iCjf^lK**^ » JV 11 V ^-X-. /V A^i ^ rami >>:V' re «..UA N D N- «(Tr" aT U 3 u A OYO 0SA»0E IT" y~^r " 4 " 14 X/,'""™ DEPARTMENT OF WATER RESOURCES ' S U 3 U N I T/ SAN LUIS OBISPO COUNTY INVESTIGATION "•°"i U 3 U N I T EXISTING AND POTENTIAL GUADALUPE* WATER SUPPLY DEVELOPMENTS OCEAN 1954 SECTION OF DAM ^4. vz ,J SAOi l^k IT -" { I! " k^'v-h j\ ,"„.„„. / ™„ 1 h ts /; ^^^^^^w-t-^sir^ Pf~M 1 V r y / \\ / \ >J ,' \\ y \ •' LOCATION MAP i r" A \ z. .- / X = \ / ;, : si DEPARTMENT OF WATER RESOURCES N u > \ \ / SAN LUIS OBISPO COUNTY INVESTIGATION N / DAM --- JARRETT SHUT-IN DAM AND SADDLE ON SECTION or DAM NACIMIENTO RIVER RESERVOIR STORAGE CAPACITY OF 110.000 ACRE FEET SADDLE DAM 1954 GENERAL PLAN REST ELEV 1150 SCALE OF FEET S. ELEV. 1130' ^^ .Wvw^^mvA^^'^^^ SECTION OF DAM SV JV CREST ELEV 1150' ^ -*" --1 ^S ^ DEPARTMENT OF WATER RESOURCES \ c^ ^ 7T° °x SAN LUIS OBISPO COUNTY INVESTIGATION & - LOWER JACK DAM ON LENGTH IN FEET JACK CREEK PROFILE OF DAM RESERVOIR STORAGE CAPACITY OF 25,000 ACRE FEET LOOKING UPSTREAM 1954 DEPARTMENT OF WATER RESOURCES SAN LUIS OBISPO COUNTY INVESTIGATION SANTA RITA DAM ON SANTA RITA CREEK LENGTH IN FEET PROFILE OF DAM RESERVOIR STORAGE CAPACITY OF 15,000 ACRE FEET LOOKING UPSTREAM 1954 DEPARTMENT OF WATER RESOURCES SAN LUIS OBISPO COUNTY INVESTIGATION YELLOW HILL DAM ON '00 200 ARROYO DE LA CRUZ LENGTH IN FEET RESERVOIR STORAGE CJWftCITY OF 80,000 ACHE FEET PROFILE OF DAM 1954 LOOKING UPSTREAM DEPARTMENT OF WATER RESOURCES SAN LUIS OBISPO COUNTY INVESTIGATION WHALE ROCK DAM ON LENGTH IN TEET CREEK PROFILE Or DAM OLD LOOKING UPSTREAM RESERVOIR STORAGE CAPACITY OF 40,000 ACRE FEET 1954 PLATE 2( ~~U rT-"'c«E»T ELEV J34' TW^^^^^mW^ CONTROL VALVE HOUSE GENERAL PLAN 700 000 - \ CHEST ELEV- S3' v\ S> 3 400 n ^i ^v^- Sy ; • i.oo -i>, * r ^ '' gzzzjnzzd v ""•. "^ DEPARTMENT OF WATER RESOURCES 300 DIVISION OF RESOURCES PLANNING SAN LUIS OBISPO COUNTY INVESTIGATION 200 LOPEZ DAM 600 700 eoo ON LfNGTH IN FEET GRANDE CREEK PROFILE OF DAM ARROYO LOOKING UPSTREAM RESERVOIR STORAGE CAPACITY OF 50,000 ACRE FEET 1954 I i I i i i i i i i I i I 1 r i i i l "I r | I I I I ——i I ————————————— O UPPER RAGGED POINT LOWER JACK- CAPITAL COST IN MILLIONS OF DOLLARS RELATIONSHIP BETWEEN STORAGE CAPACITY OF RESERVOIRS AND CAPITAL COST DEPARTMENT OF WATER RESOURCES | i | i I i I i i i i I r [ I l I i i | | | i r ———I 1 ——————— SAN MIGUELITO AND JARRETT SHUT-IN SAN SIMEON BALD TOP AND UPPER RAGGED POINT o o UPPER RAGGED POINT BALD TOP 8 10 12 14 16 18 20 22 24 26 30 32 NET SAFE SEASONAL YIELD IN THOUSANDS OF ACRE— FEET RELATIONSHIP BETWEEN STORAGE CAPACITY OF RESERVOIRS AND NET SAFE SEASONAL YIELD DEPARTMENT OF WATER RESOURCES 32 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 ' ' ' ' ' ' ' 1 ' ' 1 1 ' ' ' ' 1 1 1 1 1 ' 1 1 1 1 30 — — - - - y - 26 - / - / SAN MIGUEUTO AND JARRETT SH UT-IN 24 o lL / " - 1 ° BALD TOP AND 2 3 3 o £ „SAN SIMEON h- 18 °l — -11 , o UPPER RAGGED POINT ~ _ - Itli >- 1 16 * - _, < o — e \ Ml \y */ \ o/> - \ CM/ o 6 <« 3 * ^£e^ 5 Cr 4 - £ ^ ***• X tip- - 2 - , 1 , , 1 , . 1 , - i 1 i i i I 1 , 1 , 1 , 1 , 1 , 1 . 1 1 1 I , . 1 . , 1 i 1 , 56 10 12 20 22 26 26 30 32 34 36 38 40 42 44 46 50 52 54 AVERAGE ANNUAL COST PER ACRE - FOOT OF NET SAFE SEASONAL YIELD IN DOLLARS RELATIONSHIP BETWEEN NET SAFE SEASONAL YIELD OF RESERVOIRS AND ANNUAL UNIT COST DEPARTMENT OF WATER RESOURCES v/> . .. ~..r stti TUB I AST DATE RETURN TO the circulation desk of any University of California Library or to the NORTHERN REGIONAL LIBRARY FACILITY Bldg. 400, Richmond Field Station University of California Richmond, CA 94804-4698 ALL BOOKS MAY BE RECALLED AFTER 7 DAYS 2-month loans may be renewed by calling (415)642-6753 1-year loans may be recharged by bringing books to NRLF Renewals and recharges may be made 4 days prior to due date DUE AS STAMPED BELOW OCT 26 Call Number: 30^81^ TD201 California, Dept. of C2 Water Resources, Divi- no. 18 ~rhzoi Oz > PHYSICAL SCIENCES LIBRARY 305815 3 1175 00457 5117 xZ. 111 w 12 < \s _ K \% Z BALD TOP 10